Not a bad shooter really. You can go in guns blazing, but you can also use some tactics and think a little. I have played it through twice and there are areas that I have completed certain areas in a completely different way.
Brilliant graphics, and highly scalable so you don't need a powerful rig to be able to play it.
AI is a little stupid at times. I find the soliers mostly look at what my bullets hit. This does make them a little bit easier to kill as they will all be stood in a bunch looking at a box on the floor and wondering what is making all the noise.
The second bit with the aliens is a little poor, but the first part more than makes up for it.