It's rather difficult to really know what libraries were used in that recording, but my guess is that it could be GPO mixed with some other libraries. Sounds nice!
Why so surprised at how good the recording is? Have you been to our Listening Room here recently, or the demo page at the main Garritan site? There are literally hundreds of fantastic sounding recordings users have put together.
You need to remember that when you hear a recording which doesn't sound very good to you, that's a reflection of the weakness in the user's technical chops. It can take a Lot of experience and know-how to make recordings as good as the one you've posted, but it Does happen on a regular basis. My point is, when you hear a "bad" recording, don't blame the sounds being used - but how they've been used.
Randy says it very well. It's the artist who sculpts the clay.
The timbre and attacks on the solo clarinet and bassoon, in my opinion, differ from the standard ones in GPO. That's not to say EQ and some modification of the attack envelopes couldn't have a hand here on GPO samples (it is a very well done mix). I'm not sure at all about brass. The flutter tonguing is not a standard GPO trombone articulation, however, so I also believe that there are other libraries involved.