Some things are better than others. For example: everyone seemed to agree that Vice City had a great soundtrack, yet the game world was flat and actually felt smaller compared to GTA III (even though GTA III's world was, in fact, smaller.)
GTA IV brought good things to the game, but it also obviously scaled back a lot of ambitious stuff that was in GTA: SA. GTA IV has a superior physics engine (which was fun to play with), but its more "realistic" gameplay was also seen by most as limiting the escapism that GTA: VC and GTA: SA had.
I think what's important is that every GTA game is good (except maybe London 1969), and most people can appreciate any limitations that exist in the older games.