Resident Evil 5
I later went back (with the same partner) and tackled the game again in New Game+. Like RE4 before it, RE5 is chock full of replay: this, a Hard mode, Mercenaries, and in a cool twist, a scene/chapter select. Easy way to relive fun parts of the game, and a fun way to earn easy money for weapon upgrades. Oh, and a slew of unlockable weapons, of course.
A friend and I were discussing this the other day - other than the graphical fidelity (and maybe the online co-op?), there's really nothing in RE5 that can't be done on the Wii. If it was re-done in the RE4 Wii engine, like Chop Till You Drop, it could be a near-perfect facsimile. But with point-to-shoot! Wouldn't that be cool.
Progress: Finished normal in co-op