Also Biased.
Give him an informed decision instead of
"I didn't like it, so you shouldn't either."
Fine.
Xbox Live is a great way to talk to and meet new people. When you have alot of good friends on your Friends List, you always have a fun time. I have about 5 people that I always, always, always play with/talk to. But be careful, some older games that arent monitered by Xbox Live Moderators are crawling with hackers, such as Call of Duty 5: World at War. Every other game you join, someone will have mods (it says they have Godmode and Noclip on your screen) and be a richard.
Other than that, playing Xbox Live is very worth it. Make sure you get a Mature account, or you'll be left out on alot of things, like Facebook, Zune, and Netflix (you need a Netflix account to use it). I made that mistake while getting it because I didnt think I would need to wait until I'm loving 17 to use stuff like that.
But yeah, it's great. Have fun.