I have to say I enjoyed the maps. They we're a little rought around the edges, but the overall concept was good.
I agree with the e-mail thing Tim. brought up, I picked up an e-mail and read it, but apparently I was the only one that saw it. Even if you don't show it to all players, a message of "Player X has found an e-mail printout", and then have it logged in the quest menu. I'll admit, I was being lazy, but I can see it being quite tedious have to rewrite the e-mail so everyone else can read it.
The icons too, my thought are to colour Piercing, Impact, and Fire (Green, Yellow, Red), then have the corresponding ammo the same colour, and leave blue for special items and skills blue. Also, make the weapons the Iron crate and the ammo the wood crate, this is a standard in a lot of these types of games and makes things much easier for the player.
Reloading- I believe one of our players on our team was complaining about the pump-action shotgun not reloading past 2 (the default after 1 reload I believe), and someone else didn't know how to reload either. I think the simplest thing is to have messages on both ammo and weapons, along with the "dry fire" message and hope for the best. On that note, congrats on the weapon system, by far the best I've ever seen.
One of the other things in the map that I think could be improved are the abilities. Very simplistic, and I realise it's best that way, but a slightly different set for each marine-weapon type would be different. You could give the shotgunner his impact proffeciency, then perhaps, instead of evasion, a critical strike type ability, then 2 other abilities, universal for all marines (health bonus or something, can't think of another), then exchange rifle marine's first 2 abilities to piercing profeciency and evasion, then bash or something for fire and fire proffeciency.
Overall, I enjoyed the maps, are you still planning on maknig the fourth installment?