Great, but a little slow.
The very first waves were great, struggling to keep the enemies off my wall but after I got the sniper rifle and put all my money into speed upgrades and a repair or two I became more or less invincible. After I had maxed the reload speed there were really no other upgrades I needed, had plenty of health, regen was at level two and being wasted etc. By the time I got around to buying the auto turret it was useless and still pretty expensive. This game is probably a lot different with a machine gun but I'd still recommend some tweaks to the rifle or speeding up the curve of the game somewhat. Of course please note I played medium to level 28, I'll try the hardest next time. Good game, well presented with no glaring errors I could see.