ive finished the game twice, first time was in 7.5hrs, and 2nd i really did take my time, doing all of the side quest stuff (wife, silver keys, etc etc etc) and it was only 15hr. I really agree that if there were a 50+ hr game, it could very well be the best RPG around.
Another flaw Ive found is the variety in weapons and armour. I wish it was a lil more diablo 2 like that respect. But over all, a great game, very innovative. I would give it a 8.5/10.
Now back to san andreas
