In career mode, you get songs as you progress and you don't get to play the bonus songs
in quick play, you get all the normal songs, but you have to buy the bonus songs individually from "the store" in career mode. you only have to buy the bonus songs once (ie: you don't have to buy the easy mode version, medium mode, etc.)
Beating different difficulties does unlock stuff, but it doesn't unlock songs.
As for GH1/GH2, i found that GH1 is slower paced, with shorter songs, but in general, harder than gh2.
i found that overall the techniques required for gh2 are easier than gh1, but what makes it hard is that you have to deal with a lot more notes and longer songs.
On a side note: i missed out on getting a drummania controller for $58!! the store was sold out when i found out about the sale
