Halo 3 is addictive in the way no other game is. THe multiplayer is a lot better than campaign but campaign is still fun
Another feature is theatre. This is made perfectly. You can take screenshots, upload them to bungie, record film clips, put them on your halo 3 file share. What it does well is the fact that the right trigger controls the speed. So if hold down the right trigger a little, it will play in slow motion. THe graphics are incredible and certainly are better than previous halo games.
Now for the online play. This is great. For 6 pounds or 10 dollars, you can buy the heroic map pack, if you want, but the original maps are still great. You can go into ranked matches or social matches. For each type of ranked math (i.e lone wolves, team doubles....) You have a number next to your overall halo 3 online rank. This only appears in ranked matches. In social your overall xp, which gives you your rank, is affected, but there is no ranked number, which goes up and down depending on how good you are. On social games you have the freedom to relax and chat if you have a microphone. You can also make custom games which are fun, but still aren't as good as matchmaking.