Some type of score would have been nice, but other than that, it's great! First I died because I ran out of ammo, than I started to farm the ammo spawn as much as possible. This way I've died with 372 rounds, if that can be used as a "score".
This could be expanded into a wave based survival shooter. Throw in some sentry guns and it could be a great tower defense endless survival!
Also, is the weapon based on the M41A Pulse Rifle?