It's good to see Dungeon Defenders get fixed up and put onto Steam, I tried a quick run and had no crashes (when it originally came out it crashed constantly).
Postal is another game I played when I was younger and can easily recommend you give it a go, it's well worth the money for the carnage it delivers.
Dungeon Hearts meanwhile that's a new one to me, looks interesting though, I do love RPG games. It has great visuals and the game play looks enticing, may have to give it a blast!
Icculus said this on twitter about DD and Postal:
Dungeon Defenders/linux and a heavily-upgraded Postal 1 are now on Steam! Current mood: twitter.com/icculus/status…— Ryan C. Gordon (@icculus) March 28, 2013