Rescued from developmental hell as a True Crime game by Square Enix, Sleeping Dogs is a surprising entry in the open world genre. Games with the troubled development story tend to not be solid (LA Noire was the exception to that rule) and this game did not seem to have a great deal of buzz heading in. So, how did it turn out?
First off, it being a True Crime game made little sense. It was better than the prior True Crime games and the game world is far more realized with far more things to do. Hong Kong seems well-realized (as a praise, it may not be Hong Kong, but it feels like how Hong Kong should be). Tons of small streets, opulence and slums in close proximity, and roads that are fun to drive on while not always seeming to be laid out logically.
You are Wei Shen, an investigator trying to take down a criminal mastermind by infiltrating the Triad gang and using that to help your search for a new criminal mastermind. The characters are actually decent and Wei, unlike protagonists in GTA titles, feels like a normal guy. He doesn't do sociopathic things as a rule (he does not aim to kill innocents) and his actions seem to be understandable.
Gunplay is enjoyable. The cover mechanic works decently (you can still be hit, but not regularly) and vaulting over obstacles gives you a slow-mo attack on your adversaries. You can also come into effective melee attacks. The melee attacks actually work well. You aren't overpowered, but you are powerful enough to defend yourself and defeat opponents. Tons of enemies are beatable by you, but defense is a premium. It does take cues from the Batman fighting style, which is terrific.
Even the cars handle well. It's not, say, Burnout/Forza --- but it is better than some of the Need For Speed titles and the driving in most open world titles (as good as Saints Row, better than GTA). There are a TON of cars to choose from. And there are massive differences in the cars/bikes based on their class. Traffic patterns seem to make sense which is not something one can say frequently.
The game is not super long, which is something of a disappointment. It doesn't have, say, the insane amount of side quests to do ala Red Dead Redemption (basically, you can do drug busts, sing karaoke, and solve random events while searching for assorted collectibles). You won't have a lack of things to do, but within 30 or so hours, you will have done pretty much everything. It doesn't overstay its welcome, which is a rare plus in these games, so the length isn't a total negative, however.
Even technically, the engine works brilliantly. Frame rate doesn't chug. Visuals are impressive enough on the 360 and really good on the PC. The soundtrack isn't bad. It isn't GTA, but it doesn't have a ton of highs or lows.
Sleeping Dogs is worth the time. One of the five best titles this year.