There are those that think this game shouldn't have gotten a 10 on Gamespot. I'm not one of those people.
There is simply so much to see and do in this game, that it's incredible to think that the previous games in the series seemed so big and open before, especially when GTA: San Andreas was actually on a MUCH bigger map. This game is huge, and there's stuff everywhere to do and see that it's so much more than just a collection of missions that you have to accomplish. Some people out there seem to be bored because the missions are all the same to them, but I think missions are just the tip of the iceberg here.
The mini-games are actual games in themselves, the cars have been tweaked to really take advantage of physics, the NPCs are much more fleshed out with more realistic reactions and interactions, the weapon system has improved immensely, the effects are fantastic (love the ocean waves), the cut-scenes look great due to the detailed characters, the cops are much more tenacious so it's more of a challenge to go head-to-head with them... and on and on and on.
This game is so incredibly immersive that I sometimes play just to see something new. Hop in a taxi and look around, and you'll notice something new and cool every time, whether it's an inappropriately named business sign, or a hilarious comment on one of the many radio stations, a person saying something rude while on their cellphone, or a hilarious poster hung up on a wall. There's simply so much in every corner of this game that it's amazing that it fits on a single disc. For those people that only take the game and look at how its missions stack up against those from previous games, I think they're missng a lot of what makes it fun to play this game.
I really don't think I need to get into all the features of the game, since plenty of reviews out there have gone over GTA IV in depth. But I just have to say that I think one of the reasons that we all fell in love with the (modern) GTA series is that it allows us to do things in what seems like the real world that we couldn't ever really do (without jail time). And that's where this game really shines, because it fills in even more of what it's like to live in a real city, and lets you go nuts with everything in that city. We all want to be gangsters sometimes, and with this game you get closer to that than you ever have.
The ONLY thing I think could be improved is the framerate. While it's doesn't look bad at all, there are times when the action on-screen is a little stuttery. I'm sure all the crazy effects, high-poly characters, physics calculations, and streaming textures have something to do with that. It's not a huge deal, so that's the only thing that keeps me from giving the game a 10 myself. Otherwise, this game is perfection.
Sure, I miss being able to fly planes. Sure, I miss the jetpack. Sure, I wish I could tear down the street in the Rhino again. But those aren't enough for me to think that this game is somehow bad or flawed. It's an incredibly immersive game with a living city to roam free in. And if that city is missing a jetpack or a tank, I think I'll live.