There is only one big difference and a few smaller ones between mumorpugers.
- aesthetics
- gameplay
- the business model of F2P & P2P
Mumorpugers are all basically the same thing, with my 3rd point as the biggest difference between them.
P2P MMOs are inclined towards pleasing their customers and hang on to the "the only difference between players is how much time is invested" scheme.
F2P MMOs are inclined towards exploiting the human psyche with complex psychology. They hang on to a scheme called "the only difference between players is how much money is invested (in the cash shop)".
I've played literally every mumorpuger out there (with the exception of Maple Story and those super cartoonish ones), and all the F2P ones are the same shit.
Once they start out - they're great and fun. After a few months, the developers start putting up items that give players advantages, in the cash shop.
After a few more months, the developers start putting up items that give players insane advantages, in the cash shop.
Soon, those who didn't invest money in their characters, start "whining" about the rich people who just pay up and outrank everyone who doesn't; soon, the community starts collapsing and the company notices it - so they start milking the "cash cow" even more, until the game closes down, and the company moves on to another project.
Mind you, there is some incredibly witty psychology included in those F2P mumorpugers.
P2P MMOs, on the other hand, are definately better, because they are (more) FAIR to all players. Take a look at WoW and tell me why they're doing so much better than eg. Silkroad Online.
I guess that's pretty much it.