First all, great game, I havent had such a great coop experience since Serious Sam SE.
Few ideas here & there tho.

* For Multiplayer campaigns, allow players to reserve their character, this is for those who get annoyed by some new guy who nicks their charater after getting their stats up.

* Torch, preferably slightly wider, as of now its not /much/ of a help, and flares are more useful for defensive, and pitch black areas.

* 10-12 characters, 8 at the moment is a wee bit too small, and would be nice to have it increased somewhat.

* More bugs, In variety and amount, often I feel there`s too little of them, and not much variety, plus its allways fun to slay loads of the buggers.

* Bigger maps, although ive noticed the maps are all mainly small enclosed areas, it would be nice for some more space.

* Shotgun, 3 round isnt enough, it needs at least 6 tbh.

* Whiskey Outpost map (from starship troopers), no reason apart from it would just own :p

Thats all I can think of for now.