I’m thinking something like this.
Graphics/Sound: Too close to call.
Gameplay system: They both work and are both challenging in their own right. Again, too close to call.
Story: Neither one shines. However, the dialogue in Gears is not bad while the dialogue in RE4 induces physical pain.
Variety: RE4 has more weapons, more boss fights, more challenges, and just more stuff in it.
Size: Gears is a game of normal length. RE4 is like a lifetime’s work.
Multi-player option: Gears has one. RE4 does not.
Extras: RE4 has a number of features beyond what the regular game requires, such as the Shooting Gallery and Mercenaries. Almost enough to make up for the lack of a multi-player option.
Miscellaneous: RE4 is extremely well polished in every detail. Gears imho is a notch behind. For instance, Gears sports three difficulty levels as opposed to RE4’s two. But the third of these difficulty levels is so unfair that it actually *hurts* the game.
Verdict: At the end of the day I do prefer RE4, yet either of these gems is sufficiently spankingly sweet to hold one’s attention for weeks?/months?