The game that basically put Xbox on the map.

I never played the multiplayer in its prime, so this will be about the campaign.

Man what a journey, this is one of the best FPS campaigns I've ever played through honestly. It really gives you a sense of a grand journey and that "you're saving the fucking universe" type feel.
The AI is pretty intelligent, especially for a game this old.

The gun play is pretty consistent and fluid, every battle feels good.

The level design is mostly excellent, but there are some sections of similar hallways and backtracking that can be a slog.

The aesthetic of this game is so magical, the colors and everything just go so well, and are amplified by the killer soundtrack. Seriously, every Bungie Halo has a fucking great soundtrack, I absolutely love it.

Almost every level has a very distinct vibe and nature to it, most notable the Library being dreadful, and the Warthog run being just plain awesome.

If you are a fan of the FPS genre, or video games in general, play this game, it will forever be a staple in video game history.