I haven't seen Lock, Stock...
but I loved Snatch.
I finally saw Rock n Rolla recently. A lot of people said it was pretty similar but fell a little short of Snatch, but I found it offered a fresh experience. The rocker had some great screen time, his scenes are what I refer to when I say it had a "fresh" experience. Just the feel of the film when his character is the focus.
However, most of the rest of the film I'd say does feel pretty similar to Snatch. Didn't enjoy it less because of that fact though, and I do prefer Snatch more.
But I thoroughly enjoyed Rock n Rolla for sure.