Generally, the disc songs are very easy, and a lot of the challenging metal has been blocked out. However, there are some songs that I've noticed got through and are very challenging.
Guitar - Stevie Ray Vaughn
Drums - The Who
Not sure about Vocals or Bass yet...and of course, All That Remains and the few Iron Maiden songs that made it through are tough for everyone.
What difficult songs have you noticed came through to Lego: RB?