The GTA franchise has always been awesome. No exception here but it still shares a few of the old problems.
The story in GTA 4 is as solid as ever. The characters are well done with good voice work, the city and missions have a good feel to them and for the most part I was pretty satisfied with the story. The main storyline took me about 25 hours; I mostly just focused on the missions but occasionally went out of the way and did something else (I leave the carnage until after the game). One minor issue is that some of the European accents may be a bit hard to understand (European myself so I feel a bit of a hypocrite here) and that Niko always complains about money in the storyline, which is ironic cause you really never need it all that much.
One of the best improvements in the new game is that they fixed a good amount of the minor annoyances in GTA. You can now restart missions if you fail them but all the ammo you used up and health will be lost so it's not always a viable option. With a couple exceptions (last mission, ramp + bike = hell) the missions are less frustrating but it still occurs; less often but still a big pain when it happens. The autosave feature is a lifesaver although the lack of safehouses in the first island after you lose it is a bit of pain, the taxis outweigh this somewhat (instant transport).
But like I said, GTA was always just a fun game to play but always had a few issues. Well, there's still a few here and it's in the gameplay. Shooting (a problem in the past) is still a problem at times. It keeps improving but never perfect. The lock on range is improved which is good and seeing the health of enemies is a solid addition. That being said, it's still finicky. Someone will be right in your face and it'll lock onto the person behind them, moving the lock on from person to person is a bit of a pain and the cover system although a welcome addition is also not fully flushed out well. A quarter of the time you won't take the right cover that you want and sometimes you'll have one "splendid" time getting out of cover. Still, overall it is an improvement; buying weapons is now a lot quicker and easier and being able to pick up ammo from the same gun classes is definite plus. Also, the grenade system has been drastically improved and is spot on.
Some people have had issues with the new driving but after getting used to it I've grown to like it. One small problem is that the radio stations are a bit harder to hear even when maxing out the volume in the settings. Plus there seems to be a bit too many of the in-game commercials now. Walking on the other hand feels quite sluggish and got me a long time to get used to. You walk by default (instead of jogging) which is a pain in the ass and Niko takes a while to turn around although I like how you don't run out of stamina now. That being said the jumping has been drastically improved. Another minus is how awkwardly the controls are mapped onto the controller. Not a huge issue but it took me almost over half the game to get hang of the controls 100%.
The physics in the game are really cool. Running over people has never felt the same and it's very satisfying when you shoot a cop in the legs with a shotgun and he actually flips forward off his feet. The graphics are spot on but it's paid a bit with the performance. It's not unbearable and it's pretty consistent but the consistency's average isn't great. At first I couldn't get over it but then I just forgot about it and its forgivable when you look at the big world you're in.
GTA 4 is a great game, don't get me wrong. I loved GTA and I still love GTA, I always have and probably always will. But… it's always had its frustrating moments and they still exist here. The relationship system is something I'm totally not interested in (I just started ignoring all the "friendship" calls after a while) and the new cop system makes it frustrating to get away from 1-2 stars as it's totally random how many cops are on you (once, with one star I had a helicopter, 4 foot police, and 5 cop cars in such a small area). It also requires you to have a decent car to get away from the cops, that being said when you do, it is easier. You can say a lot of good and bad things about GTA but it does one very important thing: its fun. It's just a fun game to play, fun to run around and shoot people, fun to race, fun to just get in a helicopter and jump off in the middle of the city and more often than not, its plain old good fun action.