There's a lot of people saying GTA IV, and since GTA V's come out, I can see why. IV was supposed to be a huge step forward from the trilogy of GTA III, and graphically it was (although lack of antialiasing gave the game a real jaggedy jaggedness), but in reality it was mainly a series of minor mechanical improvements to III/Vice City/San Andreas. It was like they'd taken III and given it a makeover via bug lists and burndown charts. Sure, maps, collision detection, physics, animation, controls, and modelling must have had their own headings on the dev whiteboard, but really IV should have been a ground-up game using the lessons learned from the previous games, rather than a new iteration of an existing game with shiny new graphics.
They failed to improve where the series was really lacking: a good script for a start. Vice City and San Andreas had had very strong protagonists, with deep characterisation, but great voice acting can't cover up the crappiness of the woefully shoddy dialogue. IV was no different; you literally spend 45 seconds silent in a car before a woman who's never met you before says "you look like a guy I could really get to know better!" in a style known as wooden ham. The Slavic way of never using the definite article ("where is ladies with big titties?") got pretty tiring pretty fast. The introduction was a lesson in what not to do when writing a story: it was just a list of "here's the safehouse, here's the girlfriend's house, and here's the bowling alley, now how do we get the player from one to the other in the shortest amount of time?" Show, fellas, don't tell.
Stylistically speaking, it hadn't the neon 80s machismo of Vice City with its new wave Sonny/Rico rolled-sleeve suits and jetskis, nor the Summer-of-Spike-Lee grime of San Andreas; it came across as a mishmash of a roaring-twenties-era industrial juggernaut, but with 50s muscle cars and Dragnet-era police cars sharing tarmac with Nokia-wielding soccer moms in SUVs. All in all, a hodgepodge of styles and eras that grates badly.
Whilst we've rarely sympathised with main characters in any of the series, at least there was the boundary-pushing gaming world to immerse oneself in; all three of the III games expanded the universe exponentially, and were new places to get lost in. IV doesn't feel that much bigger. It feels more cluttered. The roads are cramped, the traffic dumb and heavy, and the vehicular physics--cars feel like they have zero weight and seem to skate along the streets--aren't suited to the labyrinthine corridor-like streets of Liberty City. This annoyed me, and I never really put my finger on it 'til I played V: cars in V feel oh-so-much heavier, with real heft and drag to them. With nearly any vehicle in the game, you can sense the weight and torque the moment you get out of first gear. Pick up a good speed and feel the thrill of driving half-a-tonne of steel, as you wend in and out across long, wide roads; real excitement not captured since an early Need for Speed game. IV is a lesson in braking sharply for every turn, because your car's going to spin around like Bambi on ice in ballerina shoes the moment you hit 30 knots-per-hour, and take an age to come to a stop. 50-yard stopping distances might be more how driving in real life works, but realism in driving is boring; you want excitement in a game like this; cars that pack a punch and make a crunch, not slippy-slidey skatey weightless physics.
I only got a few hours into it, myself. Having completed Vice City at 100%, and spent all of summer 2004 on my uni mate's PS2 for San Andreas, it's surprising at how little I cared for IV. It was just III remade with a new graphics engine. V was such a massive departing from all of that, which is why I think the series got back on track after going dangerously stagnant with IV.