I'm only seven chapters in, but this story so far is beautiful (art), engaging, and makes use of very interesting characters with interesting dynamics between them (for example, watching Alex try to interact with Nic, who is deaf and uses sign language to communicate, is extremely heartwarming).
The only thing that's got me confused is how extremely similar it is to another manga I've loved for years, Dogs: Bullets & Carnage. Nic and Worrick are basically carbon copies of Heine and Badou, right down to the fear/avoidance of women and eyepatch respectively. Even the reason Heine and Nic avoid women appears to be the same. It's really a weird thing to watch since I suspend my disbelief for a lot of it, saying it's not like Dogs has a claim on those character traits or anything. And I still enjoy Gangsta enough to ignore them, but so far it feels like similarity after similarity keeps piling on until it's gotten downright impossible to ignore.
But hey, if you're like me and love Dogs, this is enjoyable because it's different in enough ways to make it stand on its own. It's something like a different take on the "guns-for-hire with a dark past" type of story. You've got the two sidekicks with a story that unfolds a little differently, and both can be enjoyed as two separate stories existing in very similar genres if you want to think of it that way. But, again, if you happen to love Dogs and Dogs' characters, there's no reason you wouldn't love this when the two are basically the same in that respect.
Oh, and on that note, if you can handle Dogs' haphazard storytelling, Gangsta is pretty easy to understand. It doesn't reveal everything at once, but I haven't had a single problem following what's going on, so I don't really get kichiX's complaint in that regard. I had to go back and reread Dogs from volume 1 to really understand what was going on at certain points, but Gangsta so far is easily accessible even though it goes into darker topics than Dogs does.
Anyway, try it out if you enjoy dark dystopian settings and complex, adult characters. It's got enough light comedy to keep everything from being overbearingly depressing, and the characters are very engaging and unique (Dogs similarities notwithstanding), so anyone interested in any genre it fits into should come away satisfied.