I like The Black Hack, and I think The Cthulhu Hack is a good read for combining a simple ruleset with a bit of focused setting and tone. Of all of the *Hack products I've seen so far, The Cat Hack has hit me the most as a game that I want to run. In 16 pages you've got rules, a theme, some neat innovations around equipment, magic and more. The classes are really clever, and not just feline versions of fighters, rogues and so on. The Cat Hack stands out to me as something to be explored - you could read it once quickly and miss a lot. If you get it, take your time when you read it, there is a lot of really neat stuff in there.
I'm going to run it sooner or later; I have a particular setting in mind for a game of it though. I like The Walking Dead and real-world zombie fiction, and there's something neat in my mind of mashing that with The Cat Hack. The dead rise, the humans in a neighbourhood are scared and wondering what to do when Mr Jones starts snarling and chasing after his wife with blood running down his face - and a group of cats work to try and help their owners escape and survive. I've no idea where it would go in play, although I would lean on it as being serious rather than a comedy game (even though the PCs would be semi-mystical cats).
I want to find out how well it might work for a setting. I have a three week gap in my "working away" schedule coming up, so if I can find a good day there, I might try to run it on G+/Hangouts. Stay tuned, drop me an email or comment if you're interested.
And check out The Cat Hack: it's small and perfectly formed, interesting and innovative and it's $1.95 on DTRPG! Total bargain!