Generally fun!
Level 8 was quite long, gun stats would certainly be nice, especially when summing up whether or not the upgrade was worth it... Ooh, and some zombie bios! I'm a sucker for monsters.
I think level 9 was my favourite... The one with 4 respawn points where you can basically walk in a square and pick them off? Which reminds me; respawn points could be a bit clearer. Early on in some levels I stood on some by accident (blood is also red, they camouflaged).
The whole thing could have been simpler but I'm sure the extra weapons up the replay value... How about some medals?