I bought my HRD back in 1996 just after they first came out. The first thing to say is if you cant turn it up - dont bother - like most valve amps it doesnt sound great unless the power section gets worked - and that means turning it up over 4 on either channel.
I'd recommend a Dr.Z airbrake attenuator if like me you want to use this at home!
The clean channel is excellent - warm, crisp ringing tones with a nice fuzzy overdrive as it starts to break up around 11 oclock, moving through to a heavily overdriven, but quite harsh drive as you turn it up towards maximum. Theres quite a bit of headroom on the clean channel too and the amp reacts well as you change your picking strength & style.
The spring reverb unit is superb and adds more dynamics to the sound of the amp.
The basic sound of the stock amp is great for cleaner blues tones but its well documented that the amp isnt best suited for heavy rock tones in its default configuration - a marshall is more that sort of thing. The drive channels can give you a bit of extra bit to the clean channels crunch, but can get a bit harsh as you turn the gain up.
Fortunately you can get some excellent replacement tube and speaker kits that will tune the amp more toward a particular style at a reasonable cost.
Build quality on mine is very good - its very solid and youre advised to avoid climbing stairs with it!
Overall an excellent amp for those typical fender clean tones.