The best out of the halo saga to date.
Campaign: The halo 2 campaign is legendary, it improved on the original halo:combat evolved with better AI, level design, more memorable moments and a wider range of weapons. The action is always intense and you never know what the enemy is going to throw at you next. You still play as the badass Master Chief but, you will also get to play as an elite during the campaign.
Multiplayer: Halo 2 has co-op which meant I had tons of fun playing it with my friends. The multilayer is extremely addictive with brilliantly designed maps and game modes.
Graphics: For a game released in 2004 the graphics were some of the best around - clean frame rate and beautiful explosions.
Music/voice acting: The background music fits perfectly with the game, and the voice acting is good enough to be in a Hollywood film.
Controls: If you've played the first halo (or any other halo) the controls are mostly the same and you will get the hang of it in no time.
If you've never played halo or have just played the recent ones, I recommend you get this one. Trust me you won't be disappointed.