May be the start of something interesting
First off, it's pretty promising, and it definitely promises to develop into something great in future.
However, a few things do cripple the overall experience.
Firstly, and the most obvious, is the voice acting. Generally it was too forced, trying too hard to sound tough, and the attempt at imitating action movie stereotypes is too obvious. Instead, it would probably be better to try to relax it a bit, make it sound a bit more natural. It would also help if you left out the one-liners, which are really quite cheesy, to be honest. Unless you're intentionally going for the cheesy kind of atmosphere, of course.
Secondly, there are some consistency and balance issues. While I can understand the rather quick RPG sections, and how sometimes cover can be unavailable, but I found the last part to be a bit off. It difficulty seemed to contrived, created by intentionally breaking the rules. Sniping without cover, enemies popping in without ceremony and firing without any indication, and the fact that they can hit you from a sniper-rifle distance, all seemed out of place. Toward the end I found it more necessary to memorize the locations of the enemies than to try to react to their appearance. It just seemed unnecessary.
Perhaps you could have made cover allowed (since you *are* in a building), but set a time limit to clear the enemies? It would fit better in the context of the game, seeing as how you are trying to get evacuated but are surrounded. The evac chopper would have been forced to leave you behind if you took too long to clear the area.
In any case, it shows promise, and with some improvements to the consistency of the mechanics and atmosphere, would no doubt elevate to greatness.