Grand Theft Auto is a lot of things, but perfect certainly isn't one of them. It's hard to complain given the massive amount of content that the game gives you for $60, but I'm going to anyway.
1) GTA: Online is Borked
Maybe this will get fixed, heck, maybe it's been fixed by the time this gets published, but GTA: Online doesn't work. As of time of writing GTAO is a buggy, lock up prone, slow mess. Any attempt to play it is met with loading screens and error messages. I know its a big undertaking, and a lot of games have problems at launch, but GTAO didn't launch with the game. Please fix this.
2) The characters are awful
Nico wasn't exactly a font of personality in GTAIV, but at least he was sympathetic. Franklin, Michael and Trevor are equal parts boring, and unlikable. It's hard to care what happens to these people's lives when I hat everyone in them. There's no Roman, Brucie, or Woozie to root for, and it taints a lot of them game.
3) The story is meandering
It's hard to talk about this without spoiling the story, but there are a lot of plot threads going around in GTAV, but almost none of them go anywhere. Previous GTA games would weave these into a tapestry, but this one just ties them into a knot.
4) You're punished for having fun
I've lost count the number of times I tried to set up some sort of wacky or hilarious circumstance in the game, only to be murdered by the games physics engine. You simply can't do anything fun without being instantly killed.
5) Did I mention the characters
Christ I hate the people in this game. The worst of all is Micheal's family. Michael should have faked his death again and left those mongrels in a burning building.