I finished the game (well, the story missions; I still have 16 of a total of 30 jobs to complete, plus 4 or 5 events, not to mention finding the rest of the lock boxes and completing the item collections) in a little over 25 hours.
The game is a blast to play. I was actually a bit "sad" when the game was over, since I could see myself playing quite a few hours more. I'm still going to continue playing, to complete the rest of the content.
I know it's probably too much to expect, but I hope any future DLC can add a mission or two.