A review of your own gamemode? Wow, that's interesting.
Anyway, my opinion on this:
1. It's a good idea.
2. I like the idea of not knowing an alien until he/she/it:D transforms, but it seems a little unfair. See suggestions below.
3. For humans, I do think "have a shower or die" is stupid. Try more things like "the water you drank was poisonous, get treatment". Unique things.
4. If you actually WANT them to have stupid needs, try stuff like "your teammate hates you, seek therapy". Make it obvious it's a joke.
5. For the alien, the idea of how they look at you is interesting. Problem is, he goes behind you, transforms, whoops, you're dead. Not good. Make it so that there is something more than just looks.
6. For example, make the alien have needs. However, they should be different from human needs. Things that the humans would never need/want to do. An example, maybe, would be that they need a special "sludge" or toxin to survive. There will be pools of toxins around the place, that hurt people but keep the alien alive. Try things like that.
7. Not sure what you look like when you're an alien, but if it's just a burnt human.... no. Try using antlions. I think that would be really cool.
8. How do they transform? Is it just a fog around them, an actual model-to-model morph, a haze, an explosion, lights, fireworks, WHAT?!?!?!?
9. Make your description suspenseful. Eg. try this:
You creep down the dark, dingy hallway, eyes darting. A movement catches your eye, you dart forth, to find only darkness. You check that your group members are still there. They look as nervous as you, but are ready to back you up nonetheless.
Just as you turn, a green fog fills the hallway. Screams ring out, shouts are heard, loud, then quiet, a strange tune that pulses through all, bringing forth the scariest sights, then a flash- it is among us.
That's more suspenseful, right?
Well, hope you find these suggestions useful. If you use that bit I wrote, please credit me. It's mainly just inspiration, though. Can't wait to see how this turns out,
-Metroid48