This concert album is the second forgotten Crimson live disc of the '70s, the first being Earthbound, which did not get reviewed on this site because very few people probably still have a copy and, frankly, nobody else needs one.
Where Earthbound was a low-quality soundboard recording by the first incarnation of the band, full of long jams that only fans would know ("Groon," "Peoria," "Earthbound"), U.S.A. loudly chronicles the live show from the second incarnation, the Larks'-Starless-Red era that fans adore. The vinyl has only six songs; the CD remaster adds "Fracture" and "Starless," two long mostly-instrumental jams.
The problem with 
U.S.A. is that it has been tampered with in the studio; instruments were later overdubbed and the production cleaned up so that it rarely sounds like a live show and more like a studio disc. This wouldn't be a huge problem, except that Crimson rarely strayed from how it performed a song (yes, the band underwent copious amounts of jamming, but those were often given different names and not parts of real songs).
As such, the versions of "Easy Money" and "Larks' Tongues In Aspic Pt. II" are louder but not necessarily better than their studio counterparts, although the latter is a fine song in any version and the proto-metal guitar riffs sound better on stage. It's a great choice to open the disc. "Lament" and "Exiles" are little more than run-throughs of the tunes; decent songs both, but hardly worth visiting on a regular basis.
The aforementioned jam is here in "Asbury Park," which had never been released and is a loose, funky instrumental that foreshadows the band's THRAK period some 20 years down the road. The lengthy guitar solos take center stage in the song, but the uptempo double-time snare-heavy drums anchor the piece, which is a nice surprise in the middle of the proceedings.
That is the main reason to give this a shot. The other main reason is the take on "21st Century Schizoid Man," Crimson's signature piece that is fantastic no matter which incarnation plays it. This version goes a lot heavier on the drums than before (Bill Bruford had left Yes to join Crimson at this time, hence the amazing work) and turns the guitars sleeker and less clanky. Plus, hearing John Wetton tackle Greg Lake's patented growl on the original is interesting, but through the use of a box he is able to almost pull it off.
But one has to be a fan to want this CD. There is really no great reason to own it otherwise, because it doesn't explain anything and it doesn't make the band more interesting than it already is. A little more derivation from the studio versions and a better selection of tracks ("The Talking Drum" should have been included, as it was on bootlegs from this period, and why only one song from "Red?") would have made this essential, but as such U.S.A. is simply passable.