I just picked up another Rivera.
I've had the KII for years, and it's been my main amp since I got it. Lots of amps have come and gone and nothing has dethroned the mighty Rivera.
So I picked up this KR55 for stupid cheap. Very similar to the KII except WAY more gain available, not quite as much low end, and an extra channel.
It mystifies me that Riveras aren't more popular. I will admit they can be tricky to dial in due to all the tonal options available, but this is also what makes them so versatile.
I also generally use a boost with mine (but then I use a boost with pretty much all my amps).