OK, get ready for my verdict!
This will contain spoilers, so I'm gonna put this into a spoiler box
[spoiler]Your architecture was pretty good, you had an overall ruined and desolate feel to your maps. Your cave in map 1 looked a bit too square for my liking, but that just takes practise in terrain. (but you have shown that you can do better in the third map
I also enjoyed how you made the player use their brain to get more critical items, such as the armour, though if you don't jump far enough it can cost you a lot in health. Also in map 2 I liked how you made the player have to use the barrel to get up higher. In map 3 a cool aspect was giving a hint through a translator message and a razorjack to kill the brutes around the corners.
On the texturing front I'd recommend scaling up the rock textures in map 1 so they don't look so obviously tiled, or add more plants onto the cave walls. Also, for future reference, I'd align terrain manually, as the align to x/y axis command can give you stretch marks (which I noticed in the cave). In map 3 there were some alcoves that had obviously been made in the 2d shape editor, that could have done with aligning. Other than that, there were no other problems, or texture misuses.
I was confused about the lighting in map 1, as it was fully lit, though I couldn't see any light sources. I would add a couple of torches on the gates etc. and light the rest with dark blue lights, to give it a dark, foreboding feel. The other two maps were better sourced, but I think a touch of colour wouldn't go amiss
Combat was pretty tough, being thrown down a hole into the midst of three gasbags (my health went down to 64 by the time I'd touched bottom) but that was resolved with the provision of a rifle and enough ammo to take them down. If I hadn't picked up the armour in map 1, I probably wouldn't have survived through to map 3, as there was not a single bit of health in the second map. Even so, by map 3, I had to reload several times when I got to the titan part.
That finally brings us to story, we are not really told much of what's actually going on, just a couple of amusing messages from space marines and Nali.[/spoiler]
Overall, though, it was an enjoyable experience, and I look forward to where you take us next