Halo 3

I think this game and Halo Reach are tied for the peak of the series in my eyes. The campaign hits all the right notes, the multiplayer is still reasonably accessible although you will encounter some pros online, and they really nailed the gameplay in this one.

The campaign in this game is incredible. The set pieces, like having to board the huge scarab vehicles, the encounters with the flood, and the escape at the end are all executed perfectly. The filler and difficulty issues from Halo 2 are gone and the story wraps up nicely. This one is good to play on heroic with some skulls or legendary without I would say.

Multiplayer has a good variety of maps and weapons, although online has some people who are a little too good for the game to be fun. If you can find a few friends and play private matches or splitscreen though, that can be a blast. There is also a bunch of community made maps and modes which can be a lot of fun too.

The Master Chief Collection is the best way to play this now.