You may have heard people talking about Glitch lately. Tiny Speck's broswer-based, 2D sidescrolling MMO made news a bit ago when word got out that Keita Takahashi, the brilliant guy behind games like Katamari Damacy and Noby Noby Boy, was involved with the game. He is now a permanent part of the Glitch dev team.
Yes, this is a browser game, and it's a free to play one, but there's no friend pestering or temptation to use real world currency. This game is totally different from what you're thinking.
Glitch in beta now, and I've been playing it for a bit. I'm still not quite sure what I'm doing in the game, but I'm having fun doing whatever it is.