The online play is what really makes this game worth it.

User Rating: 8.7 | Halo 2 XBOX
The single player is good, but it towards the middle it's kind of boring. I probably beat like 70-75% and didn't play it again for 4 or 5 months. Then when I finally did beat, I wasn't at all excited about.
If you are going to buy this game x-box live is a must. The different match types and the rankings really make the online play enjoyable for months. The match types even include unranked matchs for people that arent as gifted in halo as other. Also good for practice in your not good when a certain weapon.
Overall I this really is a good game, but I feel it's only worth it if you are going to play it on x-box live.