Boss tends to do very solid units by quality and tone, and this is no exception. They get bashed a lot for the reasons that are sometimes valid, most of the time just ridiculous. Let's not get into that, but into the pedal.
Looks-wise it's like a ramp up and update of a classic DS-1 that about everyone knows. Sounds-wise... well, it sure is a ramp up at least in options, but going into different direction. The gain structure is way more aggressive. Instead of just one tone knob you get to set highs and lows to your preference, mid frequencies being set. Of course, unit volume and distortion level knobs are also included.
The sound is big for a small box. The pedal produces pretty massive and tight high gain sound on its own without any boosting or aid from an amp's dirty channel. I'd also like to have a mid pot to tinker with, but you surely can get by without it by adjusting the lows and highs to reasonable levels in proportion to the mid frequencies available. It indeed is pretty low noise unit as advertised by the manufacturer.
Notable is also the way it handles with different tunings: in my experience it produces very usable sounds on E standard, D standard, C standard and B standard at least, probably on any guitar tuning you throw a t it. The usability is top notch, so is the build quality.
As a pedal and for what it does, it is highly recommendable unit for anyone who needs to have a pedal that can produce tight high gain sound that is clear and separates the notes on chords even on highest gain and with low noise even without any noise gating. I can easily see this as a foundation pedal for someone heavily into any precision played high gain metal, from Metalcore to Djent to Prog Heavy.
The reasons and features above are exactly the reasons why I personally don't connect with the pedal and wonder why on Earth I did purchase this even though I did know what I was buying: the sound is quite the opposite of what I like and love in music and guitar sound. I like it loose, dirty and fuzzy, and the pedal does not do any of it. It was used so little in my arsenal that I exhanged it into another after few year of very infrequent use. I'm a jackass here and the DS-1X is not.