Yeah graphics are important, but I was really thinking in terms of how much of the environment is interactive. How many of the buildings can be entered, how many stores are there, can you use phones and computers, that kind of thing.
I don't think any open-world city game has reached the level of interactivity that GTA4 has. Unlike the poster above me, I wouldn't call this game "Rockstar-quality"; Rockstar has their own personal flavor injected into their games, and that isn't present here.
That's not to say United Front's rendition of Hong Kong isn't interactive though, because it definitely is. You can buy tea and different kinds of food from street vendors. There's a large variety of clothing you can buy from clothing stores. You can go to massage parlors. You can even purchase cars from car lots, and retrieve any of your vehicles from parking garages scattered around the city which is convenient. Various side activities are located throughout the environment, like drug busts, fighting matches, horde modes, personal "favors" for NPCs, cockfighting, and a couple other things I'm probably forgetting.
On the other hand, you can't use payphones, you can't go to internet cafes to check your email and visit parody websites, and you certainly can't go to the bowling alley with your cousin. Just doesn't fit the mood of the game I guess.
Here's another thought: GTA4's interactive setting felt necessary because, IMO, the main storyline wasn't very engaging. When you don't feel like trudging along in the missions, the game has to provide something else to have meaningless fun with. On the other hand, Sleeping Dogs can get away with having a more static environment because the main missions are so intriguing. To validate my point, I have no desire to punch civilians in the face, fly off jumps in my sports car, and mow down people in a garbage truck while playing Sleeping Dogs. In GTA4 maybe I would, but in Sleeping Dogs I'm so focused on doing the missions and being a badass undercover cop that I don't care about causing chaos.
Does that make sense? I felt the same way about Saints Row 3; the campaign was so awesome in and of itself that I could forgive the less-than-interesting environment.
It in no way compares to the overall environment quality of GTA, also I find the overall setting a bit disconcerting. Maybe I just 'connect' better to GTA scenes in fake miami and US cities.
And I'll offer a different perspective by saying that games set in "familiar" settings are more boring to me than exotic environments. I'm not fan of GTA's all-American, Statue of Liberty, apple-pie hot dog setting, because it's close enough to me that I've already been there before. Playing a game based in a Chinese city on the other side of the world, contrastly, is far more fascinating.