Resident Evil used to be about sitting in a darkened room, controller in hand, slowly creeping through zombie-haunted streets, praying you had enough ammunition to make it to survive the next five minutes, and knowing you probably didn't.
In Resident Evil 5, though, the bullets fall like manna, and the goal is to run, not crawl, to your next destination, stopping only long enough to unload your sub-machine gun on the parasite-infected horde chasing you. Co-op play is built into this game's DNA, with protagonist Chris Redfield joined in his investigation by new partner (and local bioweapons expert) Sheva Alomar.
Both the PS3 and Xbox 360 allow local and online co-op, and while these modes work well, they end up feeling more like a 1990s-era arcade shooter than a zombie horror game. The horror is far more effective when playing solo; while the AI Sheva is competent, you need to rescue her far more than when a human's in control. This increases tension, replacing the need to count bullets with the desire to keep your partner alive.
The game's visuals are gorgeous, depicting a sun-drenched Africa that stands in sharp contrast to Raccoon City's dark alleyways. Though set in Africa, the game features a multi-ethnic cast of undead, somewhat tempering concerns about the white Redfield rampaging across Africa blasting away at black-skinned zombies. There's still a certain amount of racial dissonance to the game, but it tends to evaporate when the zombies' heads split open to reveal tentacled horrors.
Those hoping for a change in controls from Resident Evil 4's run-stop-shoot mechanic will be disappointed; RE5 still requires you to stop moving in order to fire on an enemy. This may frustrate first-person-shooter fans, but I found it helped generate exactly the sort of horror you feel in the movies when the hero is carefully plugging away at an approaching monster that just ... refuses ... to ... die.