Halo (both of 'em)
I've been playing Halo 2 recently, and I got to a part that reminded me why I lost interest in the first one.
Once you get to a certain part of the game (either one), it gets so difficult to advance that it's not fun anymore. Now, granted, I've never been close to being the Wizard, but gimme a break already. I guess it's back to Prince of Persia (again, either one) for me. UbiSoft gets it. Make a game that I'll want to play over and over.
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