Entertaining, but awfully repetitive and frustratingly buggy. Almost every mission, main and side, boils down to "shoot zombies," and when the piece of shit glitches out and makes it so killing zombies doesn't contribute to the progression meter, it quickly gets tiresome. At first I thought it was just the totally legitimate copy I was playing on my totally stock, totally not modded 360, but sadly a quick Google search confirmed that it was indeed just how the game is. This made the relatively simple task of attaining 100% completion a Herculean effort, and I really don't recommend doing so.
Along with the repetition come some other lazy design decisions, like the fact that, out of four types of undead, two have the unique characteristic of charging at you.
As a whole I don't think this game's entirely worthless, as I've said it's rather entertaining with a fun story and dialogue. I just wish the wrinkles had been ironed out a little, and maybe a little more variation were added.

Oh, and Blood Dragon is still the king of expandalones.