To me GTA4 was the best in the serie, just because it took more realistic approach. Story was interesting and had couple of really awesome missions, like the bank robbery, and it's the only GTA that kept me playing it and made me wish that it would have lasted little longer. It missed the end game though, which was a huge letdown.
Like i said, it's very love or hate, which Colt .45 killer's and Uurastaja's posts further demonstrates, people either loved it or it fell flat for them.
There is one obvious deviding line, and thats people who are in it for the story, and thouse who are in it for the sandbox, i'm guessing you belong to the first catagory (correct me if i'm wrong), as you only expressed interest in the games storyline, and expressed that the game was over for you when the story was over, i on the other hand am in this for the sandbox, thats the main reason i play thease games, every once in a while i'll do the missions to spice things up a bit and do something different (or to unlock stuff), but thats all the missions are to me, diversions, something else to do in the sandbox, and i'll continue playing long after the storyline is over (assuming the game has a fun sandbox).
GTA4 had no chance in hell with players like me though, because it's a pretty bad sandbox game, with not much to do, barely any variety, mechanics that are not well suited to sandboxing, and the game constantly interrupts you and says "ohh i see you are not playing a mission, then i better give you one, here, take your cousin out to see big American titties".. *sigh*, apparently, Rockstar hasen't figured out what made their games good, namely the fact that it could be a good game to both thease types of players, that it could have both a good storyline worth playing it for, and a good sandbox worth playing it for, they where allmost two games in one, and thats just brilliant! but GTA4 is just the one game, a story driven one, and you'd be mad as a hatter if you played this for its sandbox, moreso when there are good sandboxes out there like SR2 and JC2.
So the game was practically stillborn for one half of their fanbase, that's really not a smart move, and i think we can all see the logic in that, the game could have had the exact same storyline AND a better sandbox, it would not have broken the game in any way, it could only have broadened it's appeal for more players, but the story itself is also a bit of a hot potato, as it too seems to have this "love it or hate it" effect, as does it's gameplay mechanics..
I guess in some way i should commend them for taking a risk with the game and making something that is very focused, quite different from its roots, and definately knows what it wants to be.. but i can't help feeling they have missed the point of this sort of game in doing so, that they have taken a concept, the story supported sandbox game, and shoehorned it into another genre, the linear story driven shooter (but with much more driving), eh, i just don't see how this is a good GTA game, i can see how some will find it a good story driven game, certainly, if that's your bag then i can see why people would like it, that makes perfect sense to me, but i don't see it as a good GTA game, as it's practically only half of the concept at play here, the other half of the concept is so poorly exicuted that it's barely worth mention, and the game practically seems hell bend on preventing you from using that half anyway (*ring ring* lets go see titties and play darts!).