Yeah, I thought the main quest was a little short, but satisfying. It was pretty artfully done (it wasn't so short that I was disappointed, and Skyrim isn't meant to be played, necessarily, as a linear game... meaning there's a lot of room to stop between quests).
Given that, to enjoy the game, you may to side-quests or walk around (not fast travel or just explore) during the main quest, I think that random dragon encounters add that extra immersion RPers want. While this immersion may be a problem to players who fast travel and do the Quests in a WoW fashion (me, on my first character... I fastraveled everywhere and ignored everything but the main quest), I think people who truly want to "play" their character will find the main quest comfortably timed.
I had no disappointments in terms of how it played out overall. There's not much choice in how it ends*, but that's to be expected for a main quest.
*