I disagree with you, Though the main quest could have been a bit longer.
I specifically loved the ending, even though alduin wasn't as hard as I was hoping for, Killing him and watching the skies go from stormy to clear, and full of godly lights.
That right there was worth the 50 bucks I payed.

The sidequests are amazing too, And the dungeons have proven a bit challenging for me.
If you are only in it for the sidequests, You're not really a true skyrim fan.

I also like that all the fanboys think im hating on Skyrim just because i didn't like the mainquest. Skytim is a 9.5/10 for me.

I didn't like the ending at all. I was like "now, what do I do" after I killed him. It didn't have a clear ending. I liked the part of the mainquest where i had to go to this party in Solitude, it had some sneaking and stuff. I also liked the part where you had to gather the main cities to greybeards to get peace, but I think it was very boring most of the stuff. The start was boring and epic at the same time, because I had been waiting so damn long for the game.

College of Winterhold is the best Sidequest I have done so far.