Only worth it if you have LIVE
Story Missions - it's just a basiclly get from point A to B without getting kill and it fairly easy because there is lots of health pack around. There are also bonus things you can like tag over a few things, get a certain amount of head shoots, kill a certain amount of people, get __% of accuracy to get gear that you can use on your customize cop or gangsta to use on Xbox Live.
On-LIVE - there are a few type of things you can do there are Cop gets stuff from the gangsters hide out (it's like a one way CTF) or vice versa the gangsters get stuff and bring it back to there hide out ( another one way CTF). There is also a War like you chose your side cop or robber you kill each other and which ever side gets the most points win. The last type is like a turf you tag over a spot then guarding it so no one tag over it.
You can also customize 4 cops, 4 gangster to use online, and you can also customize a tag so you can write almost anything you want.
So in closing great buy if you have LIVE, mediocre rent if you don't have live