Project Roswell - Full Playthrough
Project Roswell is a lot like DEIMOS; an entirely self-contained adventure that lasts an hour or two, exploring a military base, a small but nicely put-together exterior area, and facing enemies that are just a little too easy.
Roswell doesn't have quite as dramatic a plot as DIEMOS, (or much of a plot at all for that matter) but it also doesn't have a Storage Building, which in my opinion makes for a net positive.
The goodies you can acquire throughout the mod are pretty nifty as well.
Of the various Area 51 mods on the nexus, this one is definitely my favorite.