I just spent three and a half hours questing...and I never left Vivec. Almost four hours in one city, and that's like a hundredth of the area of the game world, and that's not counting all the running around I've done in the city before, and I didn't even go to three of the cantons. This game could take me all summer to beat; I'm one of the "join every faction and get every quest" people, so I've joined groups as disparate as the Imperial Guard, the Imperial Cult, the Imperial Temple, the Mages, Fighters, and Thieves Guild, and even the Marog Tong. No one particularly likes me for that last one, I notice.
But it's fun...the game is such a timesink, it's unbelievable. Too bad it won't sell half of what Dungeon Siege will, probably, but it deserves all the success it gets. I'm still boggled by the size of the game world; it's beyond anything I've ever seen rendered into 3D.