I've had mine for about two months now, the head with vertical 2x12 cab, and a few good points have been brought out in this thread:
1) Although it has the ability to sound good at low volumes, it really sounds great opened up at 90watts in a live setting. I've found that this amp, over all others I've played, has a focus, musicality, and ability to punch through a live mix while still sounding balanced, more than any other. It really gives you a "professional" sound, and a kick-*** one to boot.
2) EL34s. If you want all the channels to sound great, I think you have to go with these. I replaced my stock 6L6s with JJs or Winged C's or something I can't remember at the moment, but what I do remember is that although it was an improvement in tone overall, the EL34s still made channels 2&3 really come to life. Sure, the 6L6s give you a better clean channel, but the 34s by no means make your cleans sound bad.
3) Read your manual. At least twice before, and once after.
4) If you have a new cab, like I did with the rectifier 2x12, make sure you give it a week of solid playing before coming to conclusions. My amp sounded like crap when I first got it, partly because of the stock tubes, but mostly because the stiff speakers. In combo with the 6L6s it sounded like bees in a can. About a week or two of playing and some new tubes later, it totally smoothed out all the harshness and fizz.
Great amp. If I'd just played it once and had to make a decision, I probably would have ditched it. But after a few months of playing around with the dials, a few reads through the manual, new tubes, and getting used to some of the differences between the sound of this amp and my Blackstars, I'm totally sold. All the modes put out some really great sounds. Hope you keep yours and get to know it.