I thought it was great. Played for in excess of 130 hours in the end before I'd finally completed the main story quest, secondary quests and daedric quests. A lot of that was exploring and general dungeon trawling.
I'm playing Mass Effect 2 now. I'm approx 30-40 hours in and I'd have to admit, I'm getting bored of it. I just don't find the story or inter galactic world as engaging. Although they're linear game, not RPG I much preferred the Dead Space games which have similarities.