Well done on the demo!

I got to Level 54 without taking any damage or anything. The only reason i didnt get any farther was because i had to leave the pc for a second and the pause menu didnt pause the game so i died lol. There was a few things i did notice though and im going to leave you some feedback. Just a few minor glitches and such, stuff i expect from a demo.
When standing in certain areas of the map, zombies will get stuck on walls and will be unable to move until you move into another part of the play area.
The crosshair is difficult to see at times because the zombies hands are about the same color and you lose it when you move over a zombie crowd.
The esc button didnt pause the game, it just brought up a menu screen in which i could escape or push done, but the zombies still moved and i could shoot still.
Once about 5-6 zombies are on the screen at the same time, the framerate dips pretty bad(i have a higher end pc), once you kill off the zombies, it returns back to normal.
The resolution at the menus arent really that detailed and its slightly blurry.(no big deal here, just a nitpick thing)
A reloading sound would be another great addition to know when you are out of ammo and not trying to keep pressing to fire.(possibly someone from the forum could rip you a reloading sound from one of the pistols

)
Possibly making the zombies faster every 10 levels or so would add to the difficulty and would make you have a real sense of being overrun and struggling to kill them before they get you.
Other than that, the game was great. Had some good TimeSplitters things added to it and for your studio's 1st game, it was well done. I hope to see more come from the project including some more levels and different game modes perhaps. Anyways, well done!