Okay, first of all...I'm mildly annoyed that I bought this game over Games on Demand and paid double what Amazon are charging!! Guess I'll know to look here next time.
Still, the annoyance is kinda canceled out by the fact that this game is just so much fun. Where GTA4, with all its gritty brown filtered realism, looks better, SR2 looks more 'alive'. It's vibrant, at times mildly cartoonish, and takes itself way less seriously. There's just so much more actually happening in the game world, that you don't care that it's not photo realistic.
One of the best features SR2 has over GTA4 is the garage system - as in, it actually has one. You can store all the neat toys you buy/steal in your garage and access them from any crib/safe house. More than that, you can customize pretty much any vehicle, San Andreas style. In fact you can customize almost anything, from your character's appearance, to your crib itself. Some of these customizations/upgrades are really just visual and don't serve much purpose but it still helps you make the game your own.
The only bad points, are frame rate, graphic issues, and pop up. The game seems to run a bit sluggish sometimes, especially during cut-scenes (although you can turn V-Sync off for them and it helps matters, if you don't mind screen tear). It just seems weird to develop a game for a console that demands more than that platform can deliver. Weird.
There are also a few things that feel a bit rushed graphically. Rain stops falling on you when you take shelter...but it also completely stops for the rest of the world until you step outside again. Not a major thing but it sorta yanks you out of the game world when you notice things like that.
And yeah, the pop up is pretty noticeable sometimes. Not just textures but whole freakin' buildings. GTA4 at least felt a lot more fluid and continuous in the way it handled the sandbox environment.
Still, like i said, SR2 counteracts all of that with enjoyment. I've played about 5 or so hours, and I'm still finding new things to do - favorite so far being the demolition derby! There are also some nice references to Red Faction: Guerrilla (another brilliant game). Even some of the building styles in the corporate areas are exactly like the Ultor buildings in RFG!
Anyway, I know this game has been out for a while, and it has a few technical issues/weird graphics problems. But otherwise it's 95% kickass and will give you many hours of enjoyment. Go buy!!