If you've seen either movie, then the other is easy to follow. Lock... has muskets, ganja and money instead of diamonds. There are enough guns and shooting raids to keep the American NRA happy for a long time. The dialogue is freewheeling, every kind of underworld rat appears in the movies, the course of events go the way of the protagonists (though Lock... is less kind than Snatch in this regard). You get a crash course in British accents, but none like the hilarious Brad Pitt version in Snatch. One will recognise some actors common to both casts, though Lock... boasts of an appearance by Sting. The story has the same kind of recipe: four guys (a little naive compared to the other "bounders") lose a game of cards due to a scam by a sleazy figure, and have to pay an obscene amount of money in a few days. Add to this, two other gangs pulling off different schemes, the usual crop of moronic thieves, one gangster and his young son (who is in training and who will be taking over the family profession). At one point their lives collide and, well, the fun begins. The soundtrack is engaging as usual.
The ending is a little more tantalising, but I still prefer Snatch. But Lock, Stock and Two Smoking Barrels is great too, so if you like Ritchie's no holds barred filmmaking, you'll like both movies.