While I believe this is the largest DLC for Sleeping Dogs, it's still quite short. There's only a handful of missions and maybe 10 activities (3 different ones.) I ran through it to 100% completion in one sitting pretty easily. It also includes 10 collectibles which are not highlighted like the collectibles in the base game, and as far as I can tell there is no way to get them to show up on your map either.

It's also one of the type of DLC that's separate from the main game. It limits your clothing and cars, and you can't gain any exp or work on any main game challenges while playing it. It uses separate save slots, though it may pull some data from your main save when you start it (I'm not entire sure about this.)

Overall not a bad DLC, but I'd recommend catching it on sale. Also a warning: contains story spoilers, so play it after you beat the main game.