It's nice to play a GTA style game that isn't set in the US, and doesn't cast you as someone who is essentially a mass murderer. Hong Kong looks lovely, particularly at night and when it's raining, and has its own special charm that only this game can offer. There's a kind of electric atmosphere to it, and it feels very alive with a sometimes impressive number of NPCs. The parkour is simple but satisfying, and doesn't get old because it isn't overused. I really like the game's focus on hand-to-hand combat and environmental attacks instead of just constant firefights; and punching, kicking, throwing people around - it all feels very intuitive and powerful. The game has a nice tonal balance too, which is kind of a middle ground between GTA IV's seriousness and Saints Row's absurdity.
Driving is the weakest part of the game. The physics aren't good, and turning in a lot of vehicles is an incremental movement, so at high speeds you'll find yourself constantly nudging the car left or right instead of smoothly steering it. Cornering feels more comfortable once you learn to make use of the handbrake more often. Don't get me started on boats though, which are so annoying to steer that at first I assumed I'd run into some kind of bug that broke my controls. It's seriously that bad. Thankfully you don't need to use them very often.
I have quite a few smaller criticisms though... It's a little buggy. The camera is sluggish. The radio stations are forgettable... A lot of the side missions are very uninspired and generic, and I wouldn't recommend trying to finish all of them, because after a certain point they're just distractions from what's actually good about the game. Fighting becomes repetitive towards the end of the game because you're just going through the same motions, and it eventually gets very easy. The regenerative health boost you get from eating food is very OP, and when you combine that with all the combat upgrades you'll start amassing, you'll power your way through the second half of the game without much trouble. The story is good, but like many open world games, the pacing is flawed.
Sleeping Dogs is greater than the sum of its parts though. There's no individual mechanic it does really well that makes it stand out from other games. The two things that come close would be hand-to-hand combat and parkour, but they've both been done better before and since. The thing is though, many different aspects of this game mesh very nicely with each other in a way that makes it more than a simple "GTA clone," and I certainly can't fault the city and its great atmosphere. What the game offers doesn't really have the staying power for its 20 - 25 hour duration, and I don't think it's going to age very well, because some things already feel very dated only six years after the initial release (and four years after this Definitive Edition.) But it's quite a unique and memorable experience that is well worth a playthrough.