Not a be all end all explanation, but its a very comprehensive discussion on why pay to win doesn't work.
If you loved Diablo 2, Path of Exile is looking very promising. Suppose to be full f2p and the passive skill tree looks simply awesome, it is enormous!
DCUO had a pretty decent F2P System, when I played it the only things on the store were cosmetics and expansion type content like new classes and missions added on to the game after it released. Not sure how it is now, that was a long time ago.
But LoL has the best system by far, despite not technically being an MMO. Doesn't take too long to unlock champions just by playing and the only things exclusive to the store are cosmetics like Skins and Icons.
I never realized how much of a debate there was to what pay to win actually was. I agree that paying for a boost is not truly pay to win, but at the same time I also agree paying to get some kind of an advantage over another player is in some ways a pay to win situation. Like paying to get an item that could be found in game, but is very difficult to find in game.
P2W is actually very rare in the western market which is why you see most of the people in this thread using it wrong. They have no experience with P2W games.
A P2W game is something where you can buy legendaries which can't be obtained through in-game means (common practice in chinese MMOs). You end up with a power advantage that can only be obtained with real life money.
Most F2P games that people are calling "P2W" just let you skip grinding things like leveling up enchantments, gathering crafting mats, level up faster, ect. It's convenience rather than power.
Lv40 (Firefall) Dragonfly, Mammoth, Nighthawk, Arsenal
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Lv80/85 (GW2) Thief (WoW) Rogue, Mage, Priest, Hunter, Warlock, Warrior, Death Knight, Paladin, Druid, Shaman