First of all, what I liked: The art is clean and the introduction sequence sets the mood very well (even if the writing isn't exactly riveting - it does its job.)
Now, my gripes:
There were some big issues with collision detection - getting stuck on walls and ceilings during jumps and going THROUGH the walls and floors at times... definitely very frustrating in a game like this. The level 2 design (camera after camera after camera) could have been a lot better designed - putting the same obstacle in that many times in a row just kills all novelty of the stealth mechanic, which at first I was really excited about.
The timer mechanic had a similar pitfall - in the first level, it works well enough (though it is a little unforgiving, requiring a high level of platforming skill in the first level is bad enough, but coupled with the bugginess of the collision, it's seriously flawed here.) In the third level, getting hit with the timer-activating laser effectively means that you cannot finish the level in time, but since it doesn't kill you, the only sensible option is to jump into a pit to restart. This approach is not a fun one - instead, this particular obstacle should either mean instant death or it should be an unavoidable part of the level design which doesn't prevent the player from finishing.
The actual game camera should not follow the vertical movement of the player so closely, as it makes landing on a platform at the same height as the last one much more frustrating than it should be - level 3 was where I gave up due to this problem in addition to falling through the floor one too many times.
There seems to be some inconsistency in the writing as well - the villain says he will blow you up at the end of the 10 second countdown, so why does it say some about releasing gas the first time you encounter the laser that starts the timer? That was a little fourth-wall breaking...
The lack of audio really hurts the atmosphere, too. As I mentioned, I couldn't bring myself to get past level 3, but from what I saw the level design could definitely use some improvement. I just noticed in your screenshot that you can duck, as well, although I don't believe that was ever explained in the game - I simply jumped past that particular obstacle.