Disgaea series (as mentioned) often clocks more than hundred of hours for those who get caught up with it. I am still playing Disgaea 2 for PSP and Disgaea 3 for PS3 at the moment.

Armored Core offers great replay value (parts etc) too but I oft have to stop after a while. The headaches that I get from moving around in the AC really can kill. Haven't try the ones for PS3 yet though, wonder if getting the mouse will make it better or not.

LoL - actually when I said AC, I was talking about Armored Core. Forgot bout Ace Combat =d