Just finished the game.
I thought the Didact boss fight was a little dumb. The story of Halo 4 is in a lot of ways very ho-hum. Most of the UNSC characters are pretty flat, the Didact isn't all that well developed and I still feel like the Covenant being here was a misstep.
All that being said I am really honestly surprised how much I liked this game in spite of its faults. I loved what they did with Cortana and Chief and just on the sheer emotion of all of that I went into the final level pumped up as hell, any game that can illicit that is doing something right. So all in all - I really enjoyed Halo 4 and looking forward much more to 5 than a week ago. Hopefully they can keep developing Chief along these lines while tightening up their larger narrative a bit.