The Behemoth's humorous platformer BattleBlock Theater will soon shed its Xbox Live Arcade exclusivity with a release on Steam. A final date hasn't been given yet, but a closed beta is tentatively planned for March 24 - 31, 2014, to give you a rough idea.
As for new features on PC, the main additions here are the ability to swap between a primary and secondary weapon, Steam Workshop support for mods, and trading/selling of weapons, prisoners, gems, and yarn by way of Steam Inventory. Sounds great to me.
I never got the feeling that BattleBlock Theater was universally loved, but I greatly enjoyed playing through the main levels. Keep in mind that it's best experienced in co-op, though.
BattleBlock Theater Coming Soon to PC! [The Behemoth]