This game was a lot of fun...until the end.
Once I got to the reactor core, and finally got all the enemies killed, it turned to a repetitious bit of "shoot enemy, hide behind corner, wait for health to recharge, repeat." I feel that having some health pickups would have made that fight a lot more fun, as it would give the player something to move to. It was overall a solid game, it just lagged there in the end.
Also, I dunno if it's supposed to happen, but after I defeated the Alien, it kept attacking while I was trying to move to the next room. I don't know if that was supposed to happen, but I died on my way and had to redo that boss fight.