51st state is not bad, but it's not really a gritty, darkly humerous film in the same vein. I'd go for something more like Sexy Beast, or Maybe Gangster Number 1.
51st State is an enjoyable film yeah, but no real substance to it.
Layer Cake is DARK! In a good way…
Rock'n'rolla is a good effort from Guy Ritchie, perhaps won't quite have the longevity of Lock Stock, but it's a good film nonetheless.
Nobody has mentioned Revolver (another Ritchie film) yet… Does everyone else hate it as much as the critics did? I really liked it… It's not easy to follow, you have to be paying attention the whole time (compared to all his other films which are pretty easy to follow), but it's another DARK film… Very sinister! My fave character in it is the Hitman, "Sorder"… Totally emotionless!
And of course when it comes to gangster films, Tarrantinos first 2 efforts, Reservoir Dogs and Pulp Fiction will always be up there amongst the best IMO. Remember watching Reservoir Dogs for the first time, when I was probably only about 14, and found the torture scene quite disturbing!