Overkill is more of a traditional light-gun shooter, whereas UC is much slower (and precision-based) than other such games.
UC is about twice as long as Overkill, if you don't count Director's Cut as a separate mode.
Both of them use the B button for shooting, although UC lets you switch it to the A button if you wish.
UC will use the nunchuk, whereas you can get through Overkill without it.
UC offers far more fanservice.
Overkill is much more of a pick-up-and-play game. It's also far more violent, and has a ton of cursing. The end parts can be...disturbing.
Overkill has a calibration setting (i.e. you shoot where you point at the screen), and can allow you to lose the cross-hairs for a more arcade-based feel. UC lacks both of those features, so where you aim is based on where you're pointing relative to the sensor bar, not the T.V.
UC has Qucik Time Events, and BOTH players must succeed to avoid getting hurt/killed by them. Overkill lacks those.
Overall, I feel that Overkill was the much stronger game, but UC is awesome if you're a big Resident Evil fan.







