I beat it too around midnight last night (played online co-op with 3 friends from start to finish).
If I had to judge it on single player alone, I might give it a 7/10. Story is nothing to write home about, completely predictable and written many times before. The game itself seemed leagues easier than the other Halo games (played on Normal, will try legendary today). The only times I died during the entire experience were from friendlies throwing grenades at me, and falling through a hole in the final sequence. Graphics are prettier, framerate is rock solid, and all that.
I'm not much into the Halo online experience (I seem to keep getting dragged back to Shadowrun for that, love the game, and great player community) but I'll give it a go soon.
I'm glad I saw the storyline wrap up, but am a little disappointed in the single player for 60$. Kind of glad I had to return two of the Limited Edition ones (due to scratched discs...) before saying screw it and picking up the regular box. Would have felt even better if I'd waited a day or two to pik it up for 52$ at Costco.