A great game, but not perfect as some have said...
Short Review:
Ups: Engaging story, simple yet addicting gameplay, large variety of cars, plenty of side quests, and a large/beautiful environment to play in.
Downs: Story is slow at first, rare (but very annoying) NPC glitches, camera angle can be difficult to control at times, not much different from previous games (will leave you with the 'been there, done that' feeling)
Long Review:
Storyline: I will say this to anyone who has started playing GTA4 and put it down within 20 minutes, THE STORY GETS MUCH BETTER. I remember when I first started this game I was extremely unimpressed with the story. You basically run small errands for you cousin, and it is only after the first few missions that things really start to pick up. Without ruining the storyline I will say that it can be very engaging at times and will possibly make your jaw drop at times. You play as Niko Bellic, a young, decisive immigrant who will stop at nothing to make a little extra cash. Niko is a very likable character, whom you will enjoy playing as after his personality begins to unfold over the course of the first few missions. His personality is what will often make the story thrilling and humorous at times. From a personal level (and many experts will agree) the plot in GTA4 is the best one of the series thus far.
Gameplay: Fans of the series will quickly notice that other than a few controls tweaks, not much about the game play has changed. You can still interact with virtually anything, and anyone. One major change that will be quickly noticed is the way in which you lose your wanted level. You no longer simply wait around for your stars to go away, but rather have a zone that you much escape from (the zone is a circle on the minimap that represents where the cops are searching for you). After you leave the 'danger zone', you simply have to wait about 5 seconds before your wanted level disappears completely. This applies for every wanted level, but be careful, the larger your wanted level, the larger the 'danger zone' becomes (thus making it harder to escape from the police). Unlike its predecessor (San Andreas), GTA4 does not give you the ability to fly airplanes, but rather only helicopters. For that matter GTA4 is a much simpler game than San Andreas, in a very good way.
You will also notice that Niko is much more 'versatile' than his predecessors. For example, the games new ability to take cover behind nearly any object makes extremely one sided gun fights more realistic. There are also many new combat techniques, such as 'blind firing' around a corner (if you don't want to stick your head out there). But we wouldn't want to make things too easy, because blind firing is much less accurate than just aiming and shooting. Niko can also jump and climb on top of nearly any object (within reason). This is one area where GTA4 shines.
Content: GTA4 is packed with extra content, and plenty to keep you busy. I won't spoil anything, but if you can't help yourself, know that the game is just as cheat friendly as ever. From infinite ammo to invulnerability, there is most certainly a cheat code for anything you want to do. If thats not your cup of tea, then start exploring. Liberty city has undergone some serious changes since we last saw it, three games ago. There are many more areas to explore, as this game has added an entirely new island.
Missions/Difficulty: This is where I think the game needs some improvement. Although they nearly wiped out any instance of timed missions (which in previous games was a huge pain), they replaced such with the frustrating sense of failure, as some of the missions (especially early on) are just not possible for many on the first try. I found myself trying the same missions over and over again, each time starting from the very beginning. Not to mention if you die the game takes a huge chunk of money out of your wallet. On the upside of things there is plenty of variety to keep you entertained, but be prepared to get frustrated as you drive all the way across town yet again to try a mission that you've attempted 5 times already.
Graphics: The city is beautiful, as one would expect when playing anything on a PS3. As the matter of fact GTA4 has one of the most incredible graphical environments that I've seen recently. The character renderings however...are not nearly as impressive. I mean they aren't bad, they just aren't what you might expect from a game of this magnitude.
Summary/Buy or Rent?: Overall GTA4 is a game worth playing. I did not go into detail on the multiplayer aspect (mostly because I have barely tried it), but even without doing so I think my conclusion is honest and firm. Rent this game, even if your a fan of the series. I say this because you may find yourself playing this game for a few days and then putting it down, never to return. Many people thing that the GTA series has simply run its course. Lets be honest, when GTA came out on the PS2, many people (myself included) spent hours on end just simply exploring and enjoying the game. Nothing has really changed in this new addition. I'm not saying it is a bad game, far from it. GTA4 is an excellent game, but one that should be rented first, just to make sure it's something worth putting some time and effort into.