After 70 hours of play (according to Steam) I finished Sleeping Dogs and all of its DLC (Year of the Snake, Nightmare in North Point, Zodiac Tournament). Although there were a few moments in the Zodiac Tournament I disliked immensely, I have to say that, overall, I loved the game. The combat is straightforward and fluid; driving is a blast; character and story are moderately cliched, but enjoyable; the city of Hong Kong is vibrant and colourful; graphics are excellent. If you take time to explore and just screw around, though, you find a lot of what you see in the picture below.
But, considering the size of the game, and the fact Wei Shen is always on the move, it's not surprising the developers (United Front Games) chose to use such assets. I certainly would not expect them to make every building and store in the city accessible. Imagine how long that would take to create and how much space and memory it would require. The game doesn't need that kind of detail and doesn't suffer without it. It's excellent, and I can't wait for United Front's next Sleeping Dogs game.