Saint's Row 2, in my opinion, is the worst open world game to have ever existed, all thanks to its handicapped, moronic and incompletable minigames that are required to do the storyline. Side Quests are SIDE quests, you shouldn't be required to suffer through them to access to real content. That's a stupid way of inflating the average playtime for your game.
As for the GTA IV/V debate, may I remind you that GTA V has a customisable hearse with a zombie for a passenger which is almost as fast as the supercars. Checkmate, Europoors.