While I agree that GTAIV did not deserve 10s across the board (9.5 would've been better), the entire premise of your argument is flawed. This statement is 100% false, and I'm surprised nobody has yet contested it's validity:
Comparatively, from what I've heard, GTAIV is much the same as GTA III, but with improved story and enhanced visuals, yet still has issues such as aggravating pop in and difficult vehicle handling.
GTAIV has improvements that are far deeper and far more compelling than just more polygons and better textures. Your interactivity with the world around you has been raised to startling levels. The way you fly through your windshield when you crash, the way your pursuers will grab onto your car door as you attempt to flee the scene, the way cops will assist you if you're being chased (assuming they don't know you started the confrontation, lol), etc. are all part of a truly fantastic gaming experience that far surpasses anything from past GTAs.
And then there's the brand new and quite robust online system, which includes multiplayer modes like Cops & Robbers, etc.
Honestly, the many improvements to GTAIV have made me seriously consider buying it (and I probably will, once I can scrounge up the cash), despite having not bought a GTA since GTAIII (which I sold just a couple of years later, and I NEVER sell games).
Since GTAIII, I've been quite the hater of the series, and after GTAIV dethroned the greatest game of all time (OoT is the greatest. Yes, this is fact) at Gamerankings, I was even more angry and hateful of the franchise. However, my experiences over the past 2-3 days have really been changing my attitude towards the game.