Singleplayer: 10 / 10. The best characters of all the GTA games, and by far (I've played them all since GTA 3).
Multiplayer: 7 / 10, I guess. Heists, the high-end money-earning activity, are not very well thought-out and get boring soon. Other activities are fun, but don't provide income or incur losses. And you'll need A LOT of money to buy nice things in this game.

#1 downside: CHEATERS. Lots and lots of them, and they do very annoying bad things to you.

#2 downside: the system requirements. My AMD HD 6950 runs it well @ 1920x1080, but I had to turn the graphics settings down enough that my pictures doesn't look as good as the screenshots (to a large extent because of no AA, but not only that).

Singleplayer: 10 / 10. The best characters of all the GTA games, and by far (I've played them all since GTA 3). Multiplayer: 7 / 10, I guess. Heists, the high-end money-earning activity, are not very well thought-out and get boring soon. Other activities are fun, but don't provide income or incur losses. And you'll need A LOT of money to buy nice things in this game. #1 downside: CHEATERS. Lots and lots of them, and they do very annoying bad things to you. #2 downside: the system requirements. My AMD HD 6950 runs it well @ 1920x1080, but I had to turn the graphics settings down enough that my pictures doesn't look as good as the screenshots (to a large extent because of no AA, but not only that).