Taken on its own terms, this is not a bad game
To get the negatives out of the way first, the storyline is weak, other than as an excuse to shoot vampires & zombies in their hundreds. The AI is basic, although some of the enemies are surprisingly agile & tough, and will give you more than a bit of trouble to put down. The boss battles are pathetically weak, really just afterthoughts. The graphics are basic and the scenery repetitive and generic. Completing some of the objectives can be frustrating in the extreme - for example, rescuing hostages in the hopspital and putting them in quarantine chamber for safekeeping, if you dont put the right hostages in the right chamber, you cant achive the objective and move on, and in the end you're forced into the absurd position of killing the misplaced hostages to put things right & complete the objective - thetre were plenty of those sort of hair-tearing moments. Arresting baddies, which you're supposed to do to get you ranking, becomes tiresome after a while especially when you're trying to arrest someone when one or two of his buddies comes out of the woodwork and start shooting again, and you end up just killing everything in sight.
That said, I found the game enjoyable to play. The combat can be fast & furious, and the enemy corpses fly around most satisfyingly when you hit them. The guns are solid and sound good (the only frustration is that you can only carry one other weapon in addition to your undroppable pistol, making for some agonising decisions over dropping & picking up your choice of secondary weapons) But basically, I just found it a plain fun game - no pretension, just run & shoot, and sometimes thats not such a bad thing.