There is a certain truth to the saying that you get what you pay for. Free2Play Facebook games are quite frequently produced on a low budget compared to MMORPGs which can cost hundreds of millions of dollars. Thus some people believe that any Facebook game necessarily must be worse than any comparable game on another platform or business model. That is not the case.
For example I recently started playing Dungeon Overlord on Facebook. Now like any game it has its flaws. But it is much, much better than the PC-game Dungeons, which just released the Dark Lord expansion. There is more gameplay and content for free in Dungeon Overlord than in Dungeons plus expansion pack together, which would set you back $60 on Steam.