I had two main issues with GTA IV ...well three actually. The first thing i noticed was that the game was very dark, and by that i mean I couldn't actually see what the hell I was doing! My TV is fine but that issue really got on my tits in the early levels.
Secondly, and it's been a while since I played the game, the controls were very awkward. It's like they fiddled around with a system that worked well in San Andreas for no good reason.
Thirdly I never actually got to the end of the game. For some reason after one of the final missions it just stopped giving me anything to do. I always thought it could have been to do with the drawn out dating missions. Just got bored and gave up.
However, this is basically a good game despite the niggles. Some of the side games were excellent. I liked how you could get pissed in the pub and then it was like a warning what happens if you drink drive! Scenery was great but quite repetitive. Some nice side games and activities.
GTA IV was not a terrible game but I wouldn't say it's the best of the series.