Thought he was going to become a shinigami, and it was going to be an open ended conclusion where it shows him in the shinigami world with a notebook doing his work from above.
I hated the ending as well. He should have won. Or there should have been a sign L survived. Or Ryuk should have saved him and it shows you actually do go to heaven if you save a humans life. Or at the very fucking least Light should have made it into the distance bleeding from his gun shot wounds.
So many ways not to fuck up the ending.. I think I would have been way more disappointed if I was watching it while they were making it, and I had to wait a week to see everything go to shit.