Astronaughty!

[Howard Day]

This is really cool! When it comes to the environment, my only suggestion is to sprinkle some brighter/more saturated elements here and there. Things like flashing lights, yellow/black warning tape, that sort of thing. Looks really neat, other than that! I really like the extremely subtle reflection of the gun on the transparent helmet. Good job.

[Lizzrd]

For the background, remove the lightest shade on the pillars, because it's very distracting.

[Photocopier]

I think the background could do with a slight tint of either dark green or purple.
also I find the perspective on the big box visually confusing.

[Elrinth]

Love where this is going.
The main char has a red space suit, can only take me back to Rad Gravity on the NES

The top roof and the background blends together damn good, perhaps too well. IE add some separator to show that that's is roof, and that's something your hero will collide with.
As everyone else says, the alien maybe needs some more detail.
Maybe the main char should have his face a bit more stuck into the helmet. I mean he doesn't have a vulture's neck, right? Maybe I'm too hung up on this and if you stick his face in the helmet more maybe it'll remove some character. I dunno. The face looks more okay in the still than in the animation.

Here's one space suit: http://www.ketzer.com/original_movie_props/bruce_willis_space_suit.html
here's another: http://www.luxurylaunches.com/entry_images/1108/05/space-suit.jpg
Not that any of those define how the best/coolest looking one should be. But incase you hadn't seen them.