The best of the series by a long shot!
Starting off in the game you end up in what looks almost like the pier from GTA 3, only with better scenery and some nice movie cut scenes. There are a lot of cars ranging from the common cars to the really expensive which for the most part are based on speed, and not handling! Other patrons on the road are still annoying by moving in front of your car going 90 and when a collision occurs, which mostly does, they still get out of their car and piss and moan at you.
Weapons are about the same as the others as well, decent amount of them and the magnum still packs a punch just like in Vice City. The change of the main character to another race all together instead of the Italian side of things also gave GTA 4 a better look at the world today as not just Tommy Vercetti is looking to make a name for himself. But Niko is more looking towards just escaping from his past which of course keeps re appearing into his future and causing him more problems including threatening his cousins businesses and his current trouble some way of life. Another great thing is that Niko is not really in your face about things but more along the lines of stay out of my way and there's no problem, unlike the other games out there.
Something that wasn't included that would have been great was the ability to mod the game, so that after it is completed the gaming community that is interested in it can keep it alive by adding more content without haven't to wait for an expansion pack. The gaming engine too is also like the other more high tech ones being created which is great to add custom things to because it can handle things which older engines couldn't really deal with.
Bottom line is, if you haven't played this you need to go pick it up!