Now you all made me remember how awesome SR2 was. I'm not saying I was completely satisfied, but that was solely the fault of my hardware (played on PC, commence hating now) and not the game itself: whenever I was driving, the whole game became stuttery and all. But it was the elements of gameplay that made it awesome: activities that were insane at first, but turned out to be rather fun (e.g. adventures in the septic tank, or shooting up everything in a certain area), loads of opportunities for having a unique game experience (character creation, customization of various things), the missions themselves, along with the cinematics, which I really liked (the Brotherhood missions were most entertaining, including a certain tattoo-related incident), and the general sandbox feel. I have yet to meet another game where your relatively skinny character goes up to a fire hydrant, tears it out of the concrete and hits people over the head with it, finally throwing it at a gang car and causing a smaller gang war in front of your humble starting safehouse.
Whenever a game starts out with the "You have nothing, you've reached rock bottom. Get out there and take it all back!" concept, I'm pretty likely to get immersed. In SR2, earning more and more money actually had a purpose, pretty much throughout the whole game. In GTA4, this concept kinda cooled down and eventually died in around the second half of the game. Whenever I played the game, I liked the beginning loads more than the part where Niko just gets a series of hit contracts and replies to each pretty much the same way. I feel that, by the end, he pretty much becomes your average GTA protagonist who just goes out there and does whatever he is told (well, in the case of Tommy Vercetti, whatever he felt like doing) without question.
Nonetheless, GTA4 is worth playing through if you like a bit of story with your game. Even though the constant activity phonecalls were a bit annoying, I liked most of the characters. And I got to know
KINO through its music stations, so it has extra personal value for me.