My Solaris arrived 2 days ago. I've spent 2-3 hours on it so far and here's what I've got to say about it.
I haven't figured out where to put it in my rig, so I have it set up in the center of my rig (no real access to any other synth). As I was playing the Solaris, I kept looking over at my OB-X thinking "you might be going up for sale soon."
If you can shell out $4500 (price just went up) for the Solaris and can wait a year or so, it will be worth the wait. The Solaris will easily replace 2-3 expensive classic synthesizers: Prophet VS for sure, P5 and/or OB-Xa maybe and PPG 2.x perhaps.
Start with the oscillators: first you select from what type of oscillator you want to use: MM (sine, tri, saw, ramp, square, modsaw, modsquare and jaws [super saw], CEM (tri, saw, pulse, and combinations of these), VS (all 96 Prophet VS waves, WT (64 Waldorf/PPG wavetables) and WAV (user samples). Up to 4 of these can be used. The oscillators can be fed into vector or rotor (kinda like vector). Then you've got filters: MM (4 LPs, 4 HPs, 2BPs, 2 BRs, comb), SSM (LP & HP), Obie (LP, HP, BP & BR), Mini and Vocal (formant). Up to 4 can be used (in serial and parallel, I think, I'm still learning the synth). 5 LFOs, 6 EGs, basic effects (phaser, chorus/flange, Delay, EQ), arpeggiator, step sequencer, joystick (for vectors or whatever you want to assign it to) and ribbon controller. All of this is really just scratching the surface. I haven't done any serious programming - just tweaking presets and making basic single osc patches.
The Solaris sounds incredible. I filmed a demo video yesterday feeding the headphone out straight into my T3i. I tried to keep checking the levels to make sure I wasn't clipping - we'll find out soon when I edit the video. Hopefully, my video's sound will be decent and not get to jacked up by YouTube's compression. There are many SoundCloud demos by users on the Solaris FaceBook page that you can check out, too.
From what I've seen and heard of the P12, it's an impressive synth. I'm sure if I hadn't already paid for my Solaris 2 years ago, I'd have serious GAS for the P12. The P12s are already available to purchase and start using.