Well as an ex-WoW player I'm being very skeptical about online games, especially MMO RPG games... I tried few games on Facebook and they all turned out to be "pay to win". Learned my lesson and moved on to Steam... same thing when it comes to FREE online games. but there are few exceptions like "RPG MO" on Steam, it's a quite decent RPG like Runescape...
Setting aside free games, there's ARK Survival Evolved +18. Survival sandbox game that is in its late stage of development and early access is already available at Steam. The problem is its monstrous system requirements: not even close to official ones, my "i7 4770. 8GB Radeon 290, 16GB DDR3, SSD" is not good enough to run the game in 20 FPS at Lowest settings. But the game hasn't been optimized yet. and I have really high hopes about ARK.
Make sure you visit youtube and watch all the ARK videos by "jackfrags"
more then 20 episodes if I remember right.