I have not played the new one yet. I played the entire game to platinum with friends on PS3. It is a lot of fun if you have a steady group to play with. The only reason I am going to get the new one is because I am going to play it with the 3 guys I played it with on PS3.
There is no campaign at all. There are just various heists you do with other people. The online community was pretty well known for having a load of douchebags playing who thought that they got more XP if they would boot someone right at the end of a heist. So while it is a blast with friends, I could never recommend the game to anyone who was just going to play with randoms.
The replay value is that you get better skills and weapons which make the heists all play different. Also, there are multiple levels of difficulty that change how the levels play. There is also a decent amount of randomness in how the levels are setup as well (location of doors or items you have to find, etc).