Even better or at least on par with Halo 2 imo.
The story is addmitedly is nothing special, but I mostly chalk that up to this essentially being "Halo 2: Part 2". Besides, the good story bits are really damn good, especially Cortana reuniting with Master Chief near the end. The gameplay and levels are as fun as ever, tho I do wish Arbiter was actually playable again instead of being relegated to an NPC. Loved the setpieces, felt a bit more bombastic than the first two. Music kicks ass, love the use of the main Halo theme.
TLDR: game is great, a very nice end to the original trilogy.