I completed Guitar Hero 3 on the Medium difficulty last night.  In all honesty, it didn't take too much effort to do, but the last set of songs were getting to be tough.  I was able to play through each song on the first try, but didn't get 100% on any of them.  I consistently hung around the 95-98% range, but the Slayer song is going to be the thorn in my side on the Hard setting...  on Medium I only got 67% on that one. 

I was concerned before picking up the game that it would be too easy.  Considering that about a quarter of the songs on Medium really got fun and were challenging to play through, I'm not concerned any more.  I'm going to tackle the Hard difficulty next...  I know I can play through the easier songs on Hard but I'm sure I'll need to really dig in and fail a few times on the harder songs.  I'm looking forward to tackling the Priestess, Muse, and Disturbed tunes... even though they aren't the most difficult.