This game needs a Zamboni!
The strategy is all in the choice of weapons. If you can survive without spending any experience until you buy the G36 assault rifle, the game becomes easier.
Graphics - the splatter effects were good, but otherwise the graphics weren't special.
Style - I like that you can actually WALK AROUND! And that the play area extends beyond what you can see at first. Few defense games have this feature. The point spending interface was nice as well.
Sound - Great weapon & zombie death effects. The ambient growling is also good.
Violence - Yes, there is lots.
Interactivity - again, it's great to move around, but once you figure out a strategy to survive the first few levels, the game quickly becomes ultra-easy. It went from intense barely-hanging-on to just hold-down-the-triger-and move back-and-forth ho-hum in the space of about 5 levels.
Humor - ZERO. Know how to fix this? (This would probably take more programming than it's worth but...) make it possible to buy a zamboni! This little vehicle will drive back and forth cleaning up the bodies and spent shells.
Suggestions - use the old GIANT STICK MAN trick. By, say, 8am of day two, have a ridiculously huge and powerful zombie show up to throw a wrench in things. It'll make planning more important and increase difficulty. Also, rather than having the level end with those one or two zombies wandering about that you have to hunt down, end the level with a big sudden swarm of 'em that appear all at once.
If the story aspect and graphics of "Last Stand" combined with the better play of this game, we'd have one hell of a zombie shooter.