Haven't played the 360 version yet (don't own or want to own an XBox), but I have invested more hours into the PS2 Culdcept than I would like to admit. My friends from high school and I still play the game when we get together--it's a great way to spend an hour, and winning cards after every game, win or lose, is icing on the cake. (I say an hour, but we have a replay saved from an epic 3-hour, 4-player match that lives on in folklore to this day.)
Does the 360 version have a story mode, or is it online only? Watching how the NPCs played Culdcept was a great help to me get started.