As you might imagine The Black Hack learns to cut corners everywhere it can. The result is an eerie mashup of the sub-genre of ultra-lite RPGs (from Fighting Fantasy to QWERP to GURPS Lite), D&D, and....oddly....Tunnels & Trolls. For example, monsters are now basically one stat (hit dice) with some notes on special attacks. From that hit die stat you can figure out their damage dealt, hit points, and almost anything else. You also advance in experience by gaining better stat numbers, also reminiscent of T&T. Some of the Black Hack expansions out there are actually solo modules converted from T&T for use with The Black Hack, too.
The game also has the players doing all the rolls in combat....when they attack, they roll to hit, and when a monster attacks them, they roll to avoid the blow. I'll be honest.....it's a neat way to do it, I guess, but not a very D&D way (to me). Still, this is less "D&D" in design so much as it is a mix of other systems with D&D trappings.
If you like really brief but surprisingly flexible systems, or you want an RPG that can hold it's own for a weekend of gaming but requires almost no space to transport, then The Black Hack is a good choice. Get the print version here, which comes with a fold-out module (Town of Sorrowset), character sheets, and cute little GM screen. If you prefer digital, it's ebook edition is eminently suited to tablets.
I can't honestly imagine myself playing this game (White Box sort of is the bottom level of my desired minimum complexity) but I can distinctly imagine my son running this for his first game in about three years. I might also feel more in tune with the spartan elegance of The Black Hack in another decade or so. Either way....if you're a fan of minimalist systems, this is worth a look. In the end, if you want to add complexity there are like a couple dozen expansions by fans on rpgnow, including more monsters, classes, genres and rules to suit to taste.