It's hard for me to think of one, because my favorites also have big flaws.
Dungeon Siege you mention - I played the first and thought it had the worst grind of any RPG I have played, though Dragon Age gives it a run. It just went on and on.
I really liked Betrayal at Krondor series at the time - not sure how it's seem now.
I had fun with old D&D RPG's, but they're basic and the idea of drawing maps on paper now, forget it. Not too tempted to do them again much - just a little.
I loved Might and Magic 6, but again it'd seem pretty primitive and hard to play now.
Loved Legend of Grimrock, but it's more a puzzle game and I didn't want to replay much.
My favorite I'd say are MMO's - the scope is quite big.
I got started on Skyrim and mean to go back to it, but it didn't grab me that much yet.
I like games like Divine Divinity and Arx Fatalis, but haven't played them in years. Also need to play the new Divine Divinity game.
One more on the list, ok two I barely started - ok 3 - Anachronox, that 'steampunk' one what is it called, and Planescape. Ya, I know. Overdue. Does the Deux Ex series count?
Been meaning to get past the first part of the first Deus Ex also, and try the rest.