It's a great project, but I'm losing interest in playing it. That's why:

1) The first ~3 rounds are pretty boring. It's not a problem in your game specifically, but in every "Horde" game like CoD: Nazi Zombies or GoW2: Horde. So that's not a big problem.

2) When only some (at least one) enemies are left, you practically have unlimited time to build your base. That's fine when you play the game the first or second time, but it gets way too repetitive and slow soon.
Suggestion: Keep enemies coming for some minutes ("infinite" amount, but limit them to ~100 simultaneously) and stop the spawning after some time. Then you have ~60 seconds to kill the rest and to (re)build your base. The next wave will start then, whether or not all enemies from the previous wave are dead (they don't die with a new wave).
When players just want to build, they should probably try Minecraft instead. Just my opinion.

3) The main part of the game, the shooting, should be improved next, please. It does not feel very good, you need some feedback that you're shooting actually.
Then, the previous weapons get useless when you find a new and better one.
You could limit the ammunition of each weapon (except the chainsaw?) to 2-3 magazines. When ammunition runs out, you need to get back to the weapon box to pick up new rounds.
Some enemies, i.e. the flying Otter-enemies, could only be killed by a special weapon (laser, railgun, ...), so you don't just stay at a single weapon box.

4) The generator needs to have more influence on the gameplay, most people I've played with didn't even know that it exists and that you have to protect it. Then, knowing it, they still did not care at all.