nicoga3000
Saint Nic
Gitaroo-man is a pretty good comparison actually. It is much like combining the attack and defense phases.
EBA/OTO being tap only makes it harder to compare though.
Each song is scored on a 1-10 difficulty curve with 5 being average. Easy is 1-4, Normal is 4-7, and Hard is 7-10
Honestly I find you should pass anything 6 or below with no trouble. Hard is where the game kicks it up.
As long as there are a good number of hard "Hard" songs, I'll be content. Thanks!