I have to agree with the consensus here; I'm not a Cans fan. It feels more like a meat-market than a night out...which can be a good thing if you're looking for meat, to be sure...it's just not my scene these days.
I've been there a few times when the atmosphere felt like a Jr. High School dance...sexually charged and immature. The venue itself is attractive and interesting, and the services is good. The prices are right, especially for the canned beers...it's just really loud and crowded and tiresome.
I agree with Francisco W. that the rooftop terrace is a nice diversion if you find yourself out with a group of people and they insist on going to Cans. It's been less crowded than the main floors when I've been there, so it's possible to breathe a bit and talk and get a different, more grown-and-sexy vibe.