I have some notes, so I'll just put it in this thread.
1) Skills - I just realized that the skill levels listed in the advancement menu are those you can (or cannot) buy, not the skill levels you currently posses. Maybe it's just me (and it's definitely a matter of opinion) but I'd prefer if this screen showed the current level. It seems more intuitive that way. I know the current skill levels are listed on the character screen (well, not really, I only found out as I was typing this) so I guess if unspent XP was listed there (which it should - and there's still plenty of room), the advancement dialogue could be merged with the character screen.
2) XP - it should be listed in the main game view, possibly between name and health bar. I hate that I have to keep checking the menu to see if I have enough to buy my skill next upgrade, with the unspent XP value being hidden in a sub-submenu (requiring 4 keys to display and then three escapes to get back in the game).
3) Acid - I think I wrote it somewhere before, but anyway: I keep stepping around alien bodies, thinking that walking across them will hurt me because of acid. The bright green colour looks dangerous. A minor health hit when walking over corpses wouldn't make it that much more difficult, but it would motivate players to kill aliens in convenient spots. Fitness could perhaps lower the damage.
4) What do the number and a bunch or coloured bars (in the bottom right corner during the game) represent? (pseudo-edit: the first two are security/millitary keys, right?)
5) Is there a "low armour" warning? I might have missed it, but I never noticed it, unlike the (ubiquitous) low health and low ammo warnings.
6) Have anybody suggested flares, to temporarily neutralize lowlight areas? I'm sure somebody already did, but what was the response? =)
7) I just had an alien pursue me throughout a level, breaking down all doors I shut in its face. No question or suggestion here - I just wanted to say how amazing it was... I need to run away from things more =)
8) Is there a way to unload guns? When I pick up a gun of the same type as I'm holding, does the one I drop get unloaded before picking up the new one? I noticed that this way I usually get only a partially loaded gun, but after reloading it, I seem to have a bit more ammo than before.
That's about it for now.