[rant]
From what I've played, I didn't like it very much. Sure, it has the best story of all the GTA games (it literally pulls you right at the start and keeps you going the whole time), but they removed so much stuff that in the end it's a much worse product. Taxi/ambulance/police/fire truck missions are gone, gangs are gone, bicycles are gone, so much stuff has been removed that it took away a lot of the fun. Not only that, but the rewards for these types of things are no where to be found. Where are the hidden packages that unlock cars and weapons that you can grab at your safe house?
The funky aiming and horrible cover system didn't help matters any either.
Honestly, they took the best free roam game out there and made it very linear, despite the physical openness of the world around you. And while the story is great (though I've heard it kind've peters out around the half way mark. I only got 6-7 hours into the game, so I couldn't say), the missions are crap. You're either bowling with your girlfriend, stealing cars, or being a chauffeur. It's terribly repetitive, and many of the missions (bowling) aren't even fun the time.
[/rant]
Edit: I think that the game is quite a bit overrated and a big step back in many areas from GTAIII/VC/SA (and I'm certainly not alone in this), and I hope that game reviewers across the board get over this sense of "ZOMG it's GTA!!1!" when it comes time to pick the GotY.
