Make the game hard again?
There are plenty of things that make WoW hard. The new naxx has never really been a joke. The gear that drops might be a bit of a joke with the new stuff that has come out, but it still is a challenging place requiring a certain level of skill on the part of the players. Stuff like the safety dance, loatheb, thaddius, grobbulus and 4 horsemen require all your players to know the battle and their part in it otherwise you will wipe. Now you can skip naxx entirely and buy gear that is beyond it, but people who go back still get their asses handed to them because they don't know how to do it.
Then we have Ulduar. I'm gonna say it: Ulduar is harder than Trial of the Crusader. It's a very challenging place. Only a small percentage of endgame players have actually seen all of ulduar, and for a good reason. Every boss has some sort of new cheezy gimmick they pull out of their hat. There is far less room for error than there is in naxx. It's pretty fun, but the gear you get out of it doesn't match the challenge level, so right now it's better to skip ulduar and move on to ToC.
By the time ToC came out, most people were frustrated with only getting so far in ulduar before the wipes caused your raid to disband. Suddenly we have a raid with no trash that can be finished in under 2 hours. Gear was great and it wasn't as hard as ulduar. Yeah, sure, you can do trial of the grand crusader for better gear and more challenge, but it was a much more accesable raid. The heroic version really ramped up the difficulty on the order of Ulduar type frustration. I would definately NOT called those 'Not that difficult'. The extra five man was pretty sweet as well.
Of Dragons:
WotLK gave us some awesome dragon battles. Obsidium Sanctuary was a great starting raid that was much easier than running naxx, and if you do it with 3 drakes up it's a real challenge. Eye of Eternity is another one you can skip, mostly because you need an item from the end of naxx to start it, but in my experience alot of raids fall apart because of two reasons: healers can't handle the healing in the whirlwinds of phase 1 and nobody knows what they are doing on the drakes in phase 3. It's as simple as that. When Onyxia went from a lvl 60 raid boss to a lvl 80 raid boss she really got buffed. She's a fun dragon fight, no doubt about it. I have some bad history with trying 25 man pugs on her (they never work).
The 'PvP' bosses:
As silly as it is having to control Wintergrasp in order to do a raid, I will say that these are pretty darn easy bosses. Oh, sure, they all have their little 'tricks' that make it so they can wipe your raid (sometimes multiple times), but they, like so many other bosses, are no sweat if you have the nessesary addons.
Can a casual gamer raid at endgame? To some extent. If you are not willing to be on for at least 4 hours a night for several nights in a row then you shouldn't be taking a spot in the raid lineup. If you don't have Deadly boss mods, Omen and Vent then you REALLY shouldn't even bother trying to raid. Endgame is still tougher than most casual gamers are willing to endure. Endgame raids vary in difficulty, but for the most part will challenge even experienced players. Communication and knowing your job helps alot in these raids, and maybe if you think all endgame raids are easy you should try playing with MORE casual players. Then you will understand my pain in the tenth attempt at mimiron for the night...
Dual specs are EXTREMELY nice. It's the little things. Sometimes you will be raiding and somebody will have to leave (say a healer) and you can't find a replacement in guild. It's nice when your pally tank can change spec right there to healadin and a warrior can step in as the tank to fill out your party. Also, some fights in a raid require two tanks, while others take only a single tank. You have alot of options and don't have to go back to a trainer and blow tons of cash to respec in the middle of a dungeon. What does get prohibative is carrying around gear sets for each of your specs. Imagine a druid, which can play feral bear, feral cat, boomkin and treant. That is 4 seperate gear sets depending on what he has in mind. Even if you had triple spec, you still need alot of divergent gear, which would clutter up your bags and bank. Dual spec works for me, any more and I'm kinda screwed.
Blizzard has been doing a great job. The quest lines for WotLK were top notch. The new areas were all pretty fun to play. 5 man content gets you ready for 10 and 25 man content. The step jump in gear was kinda funky since I stayed current on all the top end gear, and now I can buy better gear with the new emblems (while my old emblems were phased out). All and all, the game has lived up to my expectations and continues to be worth throwing money at each month. I'm looking forward to cataclysm and finally being a troll druid (trolls ROCK!). I never really had a problem with questing in desolace (I rather enjoy that place for questing) but ashzara has always been a zone that you can skip because blizzard forgot about it long ago.