I've had this for a few weeks now so it's more of a belated NAD. The clean channel is really nice and has a mid shift push/pull pot which takes it from a tweed to more blackface voicing. Blackface seems to be more my thing but both modes are really nice sounding. The ninja boost on this channel gets it into rock and roll territory but I think I'll use it for pristine cleans more often.
The dirty channel is really versatile as well. With the boost off it can do very good low medium gain tones all the way to that cranked 800 type of sound. The boost kicks it up to a modern metal level of gain. The best thing about this channel is the clarity and punch it has even with the boost on and gain cranked. The FX loop sounds great too and doesn't seem to be finicky at all about which of my pedals it likes. My amp GAS has been severely reduced since spending some time with this Rivera.