Serious Sam Revolution - Military Decay 3 (Serious) 

Here's a a three-levels campaign set in some kind of military buildings in the middle of nowhere. The third and last level alternates outdoors and indoors environments, still very cool and original (the whole thing reminded me of some Painkiller levels). The fights are all good, with the final one being quite challenging, though I played it very badly. Thanks to the creator Unwary_Thief and to Mydlak for republishing it and adding some stuff
Steam's workshop page:
steamcommunity...
I've played this map in blind run at Serious difficulty. When you see the fades, it generally means that I've died there, or that I went back somewhere to pick up some stuff or that I've reloaded 'cause I let myself be hit too much in stupid ways