First, the story line: It's simply better, and works well with the game play.
Second, the GLITCHES. So many fun glitches in this game, I'm surprised they're not patched. Some may say this makes it a worse game, but these people are wrong. How many times have you laughed at normal gameplay? How many times have you laughed at outrageous glitches?
Great huge world, the voice acting is terrible but it's fun to just mess around in the vastness, i mean the fact i still play Just Cause 2 occasionally and it was released a long time before sleeping dogs tells me it's a better game, that's how i gauge a good game from a forgettable game, and plus, sleeping dogs world was tiny i recall :(