The game is totally multiplayer orientated imho. Playing against the computer is boring, plus the ai isn't amazing. It really comes into its own with some mates or online. To me its a must have for the 360.
Theres loads of people online, don't worry about finding a fight, especially when you're starting out.
Theres hardly ever lag either, none in europe, even against americans its practically the same as offline. The only lag i've seen has actually been against uk guys, but they were probably downloading...
I don't think it matters who hosts either, if one of you is using a lot of bandwidth on something else you will both lag the same, which is, at least a lot fairer.