The base concept of the game is really good, the visuals are astonishing in high-def, the sound is great, there are literally hundreds of zombies on-screen sometimes, and the combat is extremely well executed... most of the time. The downside, though, is that there are serious flaws (IMO, of course) in the game design.
The game is timered *and* requires leveling up to complete missions; though you can ignore the timer, if you do so you won't be able to unlock the story. This leads to unforgiving gameplay on a first run-through, or exploiting the game save system to grind through a bunch of low-level missions over and over again while accumulating XP.
Also, virtually every different action possible has a separate control scheme; walking and melee, then ranged combat, then vehicles. These schemes use radically different thumbstick operations. This makes the learning curve very irregular.
The AI is not very smart, which is acceptable for the zombies but not so much for the un-zombified.
Oh, and don't bother getting the game at all if you don't have a high-def set; you won't be able to read mission instructions unless you've got at least 720p display, and even my 26" 1080i had me squinting a bit.
There's a lot of up-side to Dead Rising (lawnmowing zombies doesn't get old, ever) but there's a lot of downside too.
-- Steve