I remember Hatsworth last pretty long and being pretty damn difficult.
I only played a few levels here and there (my wife played it more than me), but I remember it being pretty easy until the last or second to last world. Then there was a huge jump in difficulty and neither my wife nor I could beat it.
According to the activity log, I've played 2 hours and 11 minutes already, and I'm only past the first stage in the second wing.
I also haven't died yet or repeated levels or anything that would slow you down overly much. So I don't really buy that the entire game can be completed 100% in 2 hours. Rushing through all levels and skipping most e-tickets and toons maybe.
http://terosclassicgaming.blogspot.com/ - Watch me beat "GEN Alien Soldier" http://www.backloggery.com/tero - My backloggery