I got this pedal back when Blackstar only made pedals -- not the amps which I'm not particularly a fan of -- and I was intrigued by the concept of a valve-driven pedal. Not surprisingly, it sounds much fuller and fatter than just about any other distortion pedal I've used. That being said, it has a very distinct sound that doesn't exactly try to be anything else (no emulation or modeling here, really, whether that's on purpose or not). It has great medium to high gain settings, hovering somewhere between the tone of the old 5150's and the Mesa Boogie Mark IV, but almost more compressed and chunky with some settings. I use this all the time for rhythm and leads, and it works great when paired with overdrive or boost pedals to get a super-saturated sound.
Despite some of the issues I have had, this still remains one of my favorite pedals I have owned. I have a solid state amp so being able to get that warm tube sound from this pedal pairs so well with my amp. It's got an amazing crunch channel and the overdrive is super cutting and really rips. I have owned 2 of these in my time, the first one had some sort of electronic defect on one of the boards and it died on me. The second one I now have is still chugging but the 16v or 22v power supplies (depending on the model you get) are a pain in the butt. Despite this the pros outweigh the cons and I still think the tone I get from it is pretty amazing and that's why I put up with it. It has definitely shaped and influenced my sound and style!
I was lucky enough to be given this for free! (A friend of mine replaced it with a Fulltone OCD for some reason) so that's a plus. It has two useful distortion settings, one of which I use for semi-transparent overdrive and the other is to blow my band mate's ear drums when they least expect it. It's a very high quality pedal and produces warm tubey goodness, it does require a 18v power supply so that shook my board up a bit...