Pros:
Customization is leetsauce
Combat is pretty gewd
Driving and cop chases is AWESOME fun
Cons:
Sometimes you'll get a very unbalanced or impossible mission.
By impossible, I mean that I was pit against 2 other players by myself, and they held in a position that I could could not see them, without them seeing me first. This is also stated above by another member.
By unbalanced, is that depending on the difference in ranks in a group, you can have a nice fight with one enemy in the group, own one, and then get horrible maimed over and over by another.