I've now had a brief play around with SSP, and compared a few of the instruments to other libraries that I own, and while it is by no means a replacement for those other libraries, I can see myself using SSP for some purposes.
At least out of the box, without external processing, I'd say it is far less of an "epic" library than APE, Damage or HZ03 (I compared it to HZ03 rather than HZ01 because SSP appears to be comprised of solo instruments). I would describe it as sounding "natural", perhaps even "intimate", but maybe a little bit "boxy" or "midrangy" at times. I'm very impressed by the round robins and good number of velocity layers ... manually playing crescendos on the snare, for example, is pretty smooth by comparison to something like Damage or Stormdrum.
In the area of articulations, it is well ahead of HZ03, though not quite up to APE's level (at least in the variety of types of hits, although it provides a few things that APE doesn't, too). The default stereo mix is quite wet, but the individual mic positions are nicely distinct from one another, with the close mic being quite dry but still wide, while the spot mic is mono and almost a desert. By mixing in a healthy amount of close and spot with lesser amounts of mid and far mics, I was able to get a sound that I was pretty pleased with overall.
In summary, the programming seems to be of a high quality, the samples are pretty decent if a little small-sounding, and the UI has the usual beauty of the Symphony Series instruments. Especially considering the bargain price I got it for (thank you NI!), it should prove to have been well worth my modest investment.
EDIT: I rendered a quick example using one fairly representative instrument, a high-tuned snare drum, against similar drums from four other libraries (APE, HZ03, Stormdrum and Damage, in that order, with SSP heard first). I tweaked the velocities a bit for each, and added a little bit of Valhalla Room to the last two since they are naturally more dry libraries. Maybe this will be helpful to someone, so here it is ...