The Heavy is a great two-channel, high-gain distortion pedal that has some unique features. Its most unique features are (a) a two-stage noise gate (with adjustable trimpot), (b) a "weight" knob which alters the character of your low end, and (c) the two-channels with common hi/low but separate gain, weight, gate, mid, mid frequency, and output level options.
I mostly play at church live but I play harder stuff at home, and I've used the Heavy for both (only on a few select songs and lead parts at church). It can give you a great scooped sound or a nice mid-driven sound, and all sorts of stuff in between. I use it on both bass and guitar, but more on guitar.
The biggest selling points of the pedal are it has a unique "heavy" sound to it. With the "weight" knob and the EQ options, you can really get that "modern down-tuned brutality," as Empress puts. Or as I might put it, you can get your djent on. The noise gate is KILLER, and the overall design is all the things Empress is great for---solid design, tons of options, almost too many.
The biggest negative is that even with the high cranked, you don't necessarily get that super-screaming top end that you might expect. I think that's more of a design choice than a flaw. The only other negative thing I could maybe say about the design is that it might be nice to have the low and high able to be voiced separately for the two channels. That's asking a lot considering what they've put into the pedal, but it would make the pedal even more powerful.
The non-design negative is that it's $300 new (although you might be able to get it for less at retailers that offer coupons, like I did). Not crazy compared to all of the other $100-200 overdrives and distortions out there, but still a pretty penny.