The first time I listened to the Schnittke Viola Concerto, I was a bit confused by it. After several listenings, however, I've really grown to love it. From a musical standpoint, it is very modern sounding, but still melodic enough to be easily enjoyed (particularly when just listening casually). I particularly like the fast second movement. There are some very interesting orchestral effects and the viola part is powerful and delightfully schizophrenic. Since the viola is so frequently type-cast as the mournful, introspective instrument, it's particularly refreshing to hear a piece where the viola puts it all out there, stylistically speaking.
Kashkashian (whose sound sometimes is a little harsh/bright for me) really shines in concertos (her Bartok is also incredible). She pretty much has the clarity of a violin, and her sound projects well in all registers. Her vibrato is a bit wide in a few spots (particularly the slow middle section of the 2nd movement), though I'm a bit torn about it (some days I dislike it... other days I think it works).
The Kancheli is pretty slow and it's one of those pieces that requires you to constantly monitor the volume (turning it up to full blast to try to hear the whisper quiet sections, only to suddenly have your ear drums exploded by an unexpected blast of fortissimo), and that irritates me as a listener. I don't really have an opinion on the piece because I haven't listened to it enough to really understand it, so maybe a more patient person would enjoy it.
I haven't heard any other recordings of this (I have seen the DVD w/ Bashmet though) so I don't have much basis for comparison. However, as a stand alone recording, I think Kashkashian's Schnittke has plenty of enjoyment to offer the listener.