I've been playing on hard, and as expected, the game just gets gradually harder, starting easy, slowly getting harder.
Well, I'm on the Battle For Your Soul section, aka Lou's Inferno.
It went like this, in order I played.
Raining Blood:
1. "••••, I that's hard."
2. "••••••, whatever, I'll come back to it"
Cliffs Of Dover:
1. Woah, I actually really like this song."
The Number Of The Beast:
1. "••••, that's a kinda hard opening."
2. "Kicked your •••."
One:
1. "OH MY GOD. WHAT THE HELL IS THIS?!?"
Followed by "OH MY GOD, MY ARM HURTS."
Raining Blood:
1. "Okay, I got this now."
2. "So only the intro is hard. Thank God."
Devil Went Down To Georgia:
1. "Haha, take THAT, Devil."
Beat it on my first try, but still a very fun fight, and the Hard chart is almost exactly the Expert chart, I believe.