I thought it was about right but one more would have been great. I would have put an ice mountain in Eldin with a mixed ice/water dungeon. It would be like a rip-off of Banjo Tooie's Hailfire peaks but I'd think it would be cool. The Fire Sanctuary was the most disappointing one on my first playthrough but even that wasn't that bad. My first impressions were something like Skyview 9, Earth 7, Lanayru 8, Ancient Cistern 9, Sandship 10, Fire Sanctuary 8, Sky Keep 10. The game seemed to keep getting better and better until the Fire Sanctuary felt just pretty good.
The only parts of the game that made me think let's get on with it weren't dungeons though. I thought the repeat battles with the Imprisoned and much of the Song of the Hero quest were a waste of time for the most part.