Although it does use the original instrumentation (flute, clarinet, bassoon, piano, and strings), this is not the original Appalachian Spring -- it is the chamber version of the -suite-. The suite cuts about 10 minutes of good material from the original, resulting in a 'lite' edition that is not necessarily an improvement. If the 'simple gifts' section, particularly its 'climax', strikes you as a bit overblown, you will prefer the full work, which puts this section in a different context. (There are chamber and orchestral versions of both the suite and the full ballet. Most recorded performances are the orchestral suite. If you are interested in the full chamber version I recommend the Copland-conducted performance on Sony: Copland conducts Copland or A Copland Celebration Vol. 1, for the full orchestral version Tilson-Thomas on RCA: Copland: Appalachian Spring; Billy the Kid; Rodeo or Aaron Copland: The Essence of America.)
The selection of pieces here gives a pretty good cross section of Copland's work, with the Latin American sketches representing his lighter side and parts of the Short Symphony hinting at the sound of his more 'difficult' works, with the other two falling somewhere between. The Symphony famously has some tricky rhythms in parts, but is not an off-puttingly complex piece by any means. It would be inaccurate to describe it as 'twelve-tonish' -- for what it's worth, the melodies and harmonies (including the dissonances) are largely diatonic. It is similar to neoclassical Stravinsky, but less emotionally oblique. Copland considered it to be one of his best works. The score used here is an arrangement for chamber orchestra by Dennis Russell Davies, which doesn't sound very different from the original. There is also the Sextet, Copland's own chamber arrangement of the piece. (If you are interested in the original orchestral version I recommend Tilson-Thomas on RCA Copland the Modernist or Aaron Copland: The Essence of America.)
As for the performances, the OCO is a very 'professional' sounding group, which implies negatives as well as positives. As far as technical execution, they are very capable -- where I find them sometimes lacking is in the expressivity department, due to glib phrasing and (usually rushed) glossing over of the more complicated rhythms. I think they are generally more successful in lighter fare, such as the Latin American sketches (the best performance here), where the musicians don't have to internalize the music so much. I don't know if this has something to do with the fact that the group has no full-time director, but I suspect it might. This shortage of involvement doesn't completely cripple Copland's music, which is already warmly communicative, but the group's Stravinsky, for example, is quite dry and, critically, lacking in rhythmic precision.
Overall, if you are interested in hearing these pieces in a chamber setting or are a fan of this ensemble, this is worth getting, but it's not an essential Copland recording (otherwise it would probably still be in print).