[DIO]

Is there any?
I get a impression that most campaigns are designed for easy~medium.

[Dilmah G]

Medium-ish

The Retail Campaign works reasonably well on all difficulties. You can play them on whatever difficulty you want really, it doesn't make a huge difference....usually. Some "DISABLE THAT BEAM CANNON ALPHA!" Objectives will become nigh on impossible because of the low refire delay on higher difficulties.