I played RE5 for some hours last night, and basically it is RE4, just with more sunshine. All my muscle memory from RE4 works perfectly, and they clearly re-used a lot of the sound effects, especially various sound cues, from RE4!
I rather like the partner thing, sure she wastes ammo etc, but she's very good about saving my butt -- it's kinda nice knowing that when I screw up to the point of death, there's a reasonable chance she'll bop along and fix things just in the nick of time. All in all, it's quite fun so far, a bit of a mogadishu vibe...
Gfx are nice, but not as big a leap over RE4 as I imagined they'd be; maybe the horsepower's going into HD (the game was clearly meant for big-screen/highres teevees -- most of the in-game text is in a font that's so small as to be almost unreadable on my smallish lowres tv...). The environments do seem to be a bit larger (or at least, less divided into sections).
But WTF happened to Chris Redfield's biceps?!