Mortal Kombat, I have both and enjoy MvC3, but that's at its basic just a massive button bash simulator, whereas MK takes pacing and some skill.
For example, I destroy my brother at MK, then I challenged him to MvC3 [which he never played before] and I got crushed because he pressed every button as fast as possible
Also MK has a story...and scantily clad womens