I had one when they first came out, and ended up trading it toward a Nitro. This goes down as my biggest gear trade blunder of all time.
Anyway, The Tre is a great amp. Very nice clean channel, and the drive channel has TONS of gain and then, a freaking switchable gain BOOST as well. Lots of low end, but not Uberschall low end. The amp has its own thing going, I found it hard to compare to other amps.
I would think that its a great amp for the "metulz" but people seems to either like or not...I think the amp isn't for everyone despite that it has gain to spare.
It doesn't really bring it a lower volumes, where it sounds kinda flubby, but get it wound up and its a different animal. People talk about the "attenuator" in the loop, but all is has is a send/return for the loop so you can really fine tune the output from the preamp, it does nothing post-power. Its helpful, since the amp goes from off to screaming loud with the most minute turn of the volume knob.
Now, I have a Herbert, Uberschall, Triple Recto and have had every version of the Peavey 5150. IMO, the Tre is more in the league of the Mesa and Peavey...not the cost is everything, but the Diezel and Bogner are very special. However, the Tre would sit with a Mesa or 5150 any day, and will A) sound more modern and have more low end than the 5150 and B) have gobs more preamp gain which makes reasonable volume playing better than the Mesa, which is IMO the WORST amp in terms of "it sounds like shit at low volume."
The cool thing about the Riveras is that they seem pretty cheap on the used market, the Tre can be found I think for under $1,400. I think that is a steal for that amp!