It's the fact that there is no DRM involved that convinced me. Client download is free, guest account is free and all your stats are online; you can reïnstall/unïnstall all you want, install it anywhere and play anywhere. I couldn't resist, just because of that.
What I don't like though is having to buy additional weapons and licenses eventualy, but I'm quite happy with the content I have now and it should get better as time goes on. You're not forced into buying additional stuff.
Playing mini-games to pass the time is great, but now there's only Breakout (or Breakthrough as it's called in-game). Fingers crossed for Pong.
Really, the quality on youtube doesn't do it justice. I packed 5 of those in an archive and am trying to put it on Filefront. It's not coöperating.