Quite an interesting game, though with some minor flaws
There was an FPS issue while running the game on my E8400 for primary benchmarks to determine the performance. I decided then to swap in my Core i7 920 + X58 motherboard (all the other parts the same), and right away, the game just ran much more smoothly.
On my E8400, my CPU load went up as high as 50-70% (yikes!), but on the Core i7, it would never go up beyond 25-28%. Also, my total frame rate went up from a measly 18 average to a cool 38, which is definitely playable.
I've determined that the majority of performance issues are resulting from the operation of Dual Cores for the game. Dual cores, while faster than quad cores, still only have 2 processing units. Grand Theft Auto 4 needs as much power as it can get, along with bandwith.
So before you critique this game, try critiquing your computer first. Does it have enough juice to run the game fluently? And compare it to an Xbox 360 or PS3. A Xbox 360 has 3 processing cores and the PS3 has 8. Obviously, that one core lacking that you have is making a big difference in terms of performance.
Apart from that, the game is fun as usual, and I can't wait for the infamous mods that will be landing.
Some of you might be mad that you'll have to pay money to upgrade, but really, if you think about it, if you are running a 2 year old processor, don't you think you should at least give the Quad's some thought now? Multithreaded games are here, and Grand Theft Auto 4 is just one of the many PC games that will be so.