A faithful recreation of one of the best games ever made
Although I've played through the original game several times, I still find the campaign of Anniversary to be refreshing. The Anniversary edition basically slaps on a fresh layer of gloss and adds terminals, achievements, and co-op to the mix. To say 343 simply added gloss is an insult. When you switch back and forth between the classic mode and remastered mode you need to really appreciate the work that went in to making this game shine. The saying if it ain't broke don't fix it applies here so I'm glad 343 did not reimagine the campaign, they simply improved upon the original.
Multiplayer:
The online component is an entirely different game. When you run multiplayer, the disc spins up Reach's online component. The multiplayer is ok. I played Reach last year so I've already experienced it. The Anniversary maps are simply a map pack for Reach owners so nothing groundbreaking here. Memories of being frustrated with Reach quickly came back to me. In five 4-on-4 multiplayer games, at least one person quit out on my team each and every time...wonderful.
Conclusion:
Is it worth $40? A short answer, yes. Love it or hate it, Halo was, and still is, one of the best games ever made.