Fully upgraded with all weapons: 2 days 17 hrs 44 min
Fastest so far: 1 day 19 hrs and 26 min... Think can beat it faster...
It's a really nice game, with a nice background story and a really nice twist at the end, but it could improve a lot.
It's pretty slow though, you could make it more challenging if there were more enemies per wave, can't grow/research while reloading, make character have levels so you couldn't just spam skill points, etc. Nevertheless, it's a good time killer. Also every other weapon, imho, is overshadowed by the sniper and the x ray gun. One can finish the game easy just by using the sniper rifle, but it's easier with the x ray gun.