Real great start, the jump's a bit floaty but otherwise handles great! Hitboxes also feel very nice so far.
The lack of any sort of weapon options is very disappointing. Throwing oxygen tanks and bricks feels really lame compared to grenades; maybe if the tanks could hit multiple enemies on the bounce it would feel better? Also, the follower ally never seems to actually do much.
If you aren't going to increase weapon variety, you'd better go real hard on enemy variety. The boss and sub bosses were real nice, and the soldiers are fine so far, but you'll need a lot more to keep people engaged over a full 5-8 levels or however many you're planning.
I can already tell I'll probably be buying the finished version, so keep up the good work!