I've been meaning to talk about this for a while. I've run about 13 levels worth of DnD 4 now (starting at level 1 to level 13), as a DM, and have done more 3.5 by far. I didn't really go into this with any bias as far as I know, but now that I've got so much experience under my belt (not infinite, but enough to make some good opinions) here are my thoughts:
1) DnD 4 Item system is really boring
This is unfortunate to me as a DM, but there it is. The balancing of the game is so rigid that very few of the items from the books are all that exciting. The original release with 'Daily Item Powers' being a weirdly limited resource was also really convoluted. The fact that as you level, you don't get 'new items' you just get slightly stronger versions of existing ones is also annoying. If I want fun itemization I need to do it myself.
2) DnD Crit system is rather a mess.
So, they had a really good idea with the 'crit just does max damage' thing. It simplified the issue and gave you a nice baseline to figure out how much damage you dealt without rolling. It was elegant, even if less impressive than previous versions crit system.
Unfortunately it was no doubt pointed out during early playtest that crits make little difference as you get further into the game. 1d6 + 15 damage isn't really much better on a crit. And so we give items an additional die roll for crits for even more damage... but now we've completely lost the elegance of the original concept. Telling a player "You crit, it deals max damage!" and then followed with "Well, except you do 2d6 more, no you have to roll that." To make matters even less interesting, you don't have many ways to improve crit chance, making them even less of an interesting aspect of the game.
3) Durations in 4e are inscrutable.
This is the one that really kills me, as a DM. Once again, someone had an honestly good idea in trying to simplify the duration of effects in the game. But by reducing them to 'until end of turn' or 'until end of encounter' you suddenly start having to keep track of many more. Because MOST are 'until (beginning) of this (target's) next turn', you have to constantly be keeping track of them.
And lets talk about 'save ends'. Another simplified concept that could have worked great, except for the fact it doesn't. The difference between 'save ends' and 'end of turn' is potentially huge. In fact, it is so polar in its POTENTIAL that you have to be VERY careful with 'save ends'. Stunned, save ends, could mean that the person does nothing for 4 turns. It isn't even THAT unlikely. So what if it means 2 turns on average. The idea of a few poor rolls completely killing a party or player is really terrible.
Not only that, but We aren't just happy with Save Ends. We add 'after effect' to make more complicated things occur. Or 'after failing the first save' type of things. Yes, we have now made the effect MORE cumbersome than it was originally. The DM needs to remember to make the save (especially for the monsters) and then has to remember the aftereffect, and if the effect changes based on serial fails. Holy jesus!
4) Gameplay is more tactical 4e
By having better defined roles in the game, the capabilities of each class are greatly increased. There are generally more options for each class to level up with, barring pure spell caster, which feel oddly castrated. The types of effects in the game are much more closely tied with actual needs in combat.
5) Move, Minor Standard is a win
3.5 definitely had a harder time communicating how much you could do in a turn, ESPECIALLY for monsters. The standardized action system helps a bunch by codifying all possible actions. Well, except for interrupts. Those are the dirty little secret of the system since it is actually "Move, Minor, Standard, Immediate" and we just don't talk about the last one.
The only glaringly missed opportunity here, is that there aren't enough cool things to do with minors. A few more 'standard' minor actions in the game would have made players more rarely have the feeling they were wasting some of their action.
6) Daily, At-will, Encounter... Utility?
It makes me sad to say it, but this just doesn't work out right. Not only do they have to constantly special case and break their rules, but they also had weird restrictions based on the effects. Why do you only get at-wills at the start of the game? Why do we label powers 'utility' powers? The number of times I've had to help someone figure out how often they can Use a Utility power is really high.
Also, by making things Once per encounter, or any number of times per encounter, we lose a level of granularity that would be nice. It is worse because of the duration situation as per my previous point. Encounter powers CANNOT HAVE 'until end of encounter' effects, because you would be able to get them during all encounters all the time, which removes the point of having a duration. So they always have at best 'save ends'.
7) Too Many Feats
I can hardly believe I'm typing this, but it's true. Going through the list of feats trying to pick one is extremely arduous if you care even a little bit. This is made worse because of how many TERRIBLE feats there are. By the time someone is choosing from the Paragon list of feats, they have more than 200 to choose from! TWO HUNDRED! And since you get so many of them, very few of them are all that much of a stand out, and most require you to remember that you have them so you can use them in combat. For experienced gamers like myself, it isn't too bad. But neophytes were having a really hard time with it.
8) Much better Monsters
4e has some weakness, but interesting monsters isn't one of them. I felt it was much MUCH easier to just pick up monsters out of books if I needed to, and play them. This is by far the biggest win of the Edition, especially as DM i concerned. I normally make my own monsters, but having the option of using a mix of off the shelf and home grown was very nice. They also were designed for a variety of tasks so there was almost always something I could use, or at least be influenced by.
Conclusion
Some good, Some bad. It was a nice change of pace, and I'm not sure if I would 'go back' to a previous version, and I'm also not sure I want to have to teach my play group another thing. So I might stick with it.
I do wish they'd done a fair bit better though.
1) DnD 4 Item system is really boring
This is unfortunate to me as a DM, but there it is. The balancing of the game is so rigid that very few of the items from the books are all that exciting. The original release with 'Daily Item Powers' being a weirdly limited resource was also really convoluted. The fact that as you level, you don't get 'new items' you just get slightly stronger versions of existing ones is also annoying. If I want fun itemization I need to do it myself.
2) DnD Crit system is rather a mess.
So, they had a really good idea with the 'crit just does max damage' thing. It simplified the issue and gave you a nice baseline to figure out how much damage you dealt without rolling. It was elegant, even if less impressive than previous versions crit system.
Unfortunately it was no doubt pointed out during early playtest that crits make little difference as you get further into the game. 1d6 + 15 damage isn't really much better on a crit. And so we give items an additional die roll for crits for even more damage... but now we've completely lost the elegance of the original concept. Telling a player "You crit, it deals max damage!" and then followed with "Well, except you do 2d6 more, no you have to roll that." To make matters even less interesting, you don't have many ways to improve crit chance, making them even less of an interesting aspect of the game.
3) Durations in 4e are inscrutable.
This is the one that really kills me, as a DM. Once again, someone had an honestly good idea in trying to simplify the duration of effects in the game. But by reducing them to 'until end of turn' or 'until end of encounter' you suddenly start having to keep track of many more. Because MOST are 'until (beginning) of this (target's) next turn', you have to constantly be keeping track of them.
And lets talk about 'save ends'. Another simplified concept that could have worked great, except for the fact it doesn't. The difference between 'save ends' and 'end of turn' is potentially huge. In fact, it is so polar in its POTENTIAL that you have to be VERY careful with 'save ends'. Stunned, save ends, could mean that the person does nothing for 4 turns. It isn't even THAT unlikely. So what if it means 2 turns on average. The idea of a few poor rolls completely killing a party or player is really terrible.
Not only that, but We aren't just happy with Save Ends. We add 'after effect' to make more complicated things occur. Or 'after failing the first save' type of things. Yes, we have now made the effect MORE cumbersome than it was originally. The DM needs to remember to make the save (especially for the monsters) and then has to remember the aftereffect, and if the effect changes based on serial fails. Holy jesus!
4) Gameplay is more tactical 4e
By having better defined roles in the game, the capabilities of each class are greatly increased. There are generally more options for each class to level up with, barring pure spell caster, which feel oddly castrated. The types of effects in the game are much more closely tied with actual needs in combat.
5) Move, Minor Standard is a win
3.5 definitely had a harder time communicating how much you could do in a turn, ESPECIALLY for monsters. The standardized action system helps a bunch by codifying all possible actions. Well, except for interrupts. Those are the dirty little secret of the system since it is actually "Move, Minor, Standard, Immediate" and we just don't talk about the last one.
The only glaringly missed opportunity here, is that there aren't enough cool things to do with minors. A few more 'standard' minor actions in the game would have made players more rarely have the feeling they were wasting some of their action.
6) Daily, At-will, Encounter... Utility?
It makes me sad to say it, but this just doesn't work out right. Not only do they have to constantly special case and break their rules, but they also had weird restrictions based on the effects. Why do you only get at-wills at the start of the game? Why do we label powers 'utility' powers? The number of times I've had to help someone figure out how often they can Use a Utility power is really high.
Also, by making things Once per encounter, or any number of times per encounter, we lose a level of granularity that would be nice. It is worse because of the duration situation as per my previous point. Encounter powers CANNOT HAVE 'until end of encounter' effects, because you would be able to get them during all encounters all the time, which removes the point of having a duration. So they always have at best 'save ends'.
7) Too Many Feats
I can hardly believe I'm typing this, but it's true. Going through the list of feats trying to pick one is extremely arduous if you care even a little bit. This is made worse because of how many TERRIBLE feats there are. By the time someone is choosing from the Paragon list of feats, they have more than 200 to choose from! TWO HUNDRED! And since you get so many of them, very few of them are all that much of a stand out, and most require you to remember that you have them so you can use them in combat. For experienced gamers like myself, it isn't too bad. But neophytes were having a really hard time with it.
8) Much better Monsters
4e has some weakness, but interesting monsters isn't one of them. I felt it was much MUCH easier to just pick up monsters out of books if I needed to, and play them. This is by far the biggest win of the Edition, especially as DM i concerned. I normally make my own monsters, but having the option of using a mix of off the shelf and home grown was very nice. They also were designed for a variety of tasks so there was almost always something I could use, or at least be influenced by.
Conclusion
Some good, Some bad. It was a nice change of pace, and I'm not sure if I would 'go back' to a previous version, and I'm also not sure I want to have to teach my play group another thing. So I might stick with it.
I do wish they'd done a fair bit better though.