I think the number and length of the dungeons was fine. Each one brought something new to the table, and were very well designed. In fact, I found the dungeon design in SS pretty incredible compared to some other LoZ dungeons that have caused nothing more than misery and turmoil (Water Temple, anyone? Both in OoT and MM
;;
However, I do believe that the amount of content outside of the dungeons was definitely lacking. The whole 3-area nonsense just flat-out bothered me. Sure, certain parts couldn't be explored until later items were obtained, etc., but it just wasn't enough. The sky was undeniably bland (in my opinion, more so than the sea.) Nothing HAPPENED out there, whereas on the Great Sea, you had giant Octorok battles and pirate ships bombarding you. In the sky you simply flew from one beacon to the other...
The Hyrule I know and love involves a wider variety of both core destinations, and land in between. I understand that this was the first in the 'timeline,' so having Link just run around an unexplored Hyrule and land down-under-the-clouds could be a little strange for story purposes in Miyamoto's eyes. For me, however, there just wasn't enough. The game worked well for what it presented, but another couple of areas would've been nice (an icy region, perhaps? Or maybe a tropical island for something different....)