So far it's a quick and painless process. I'm still new to the reviewing community, and hopefully can get more in depth once I get a guitar that can fast forward through everything. But so far, here's what I reviewed (will add group later):
"24-7" by The Pursuits (Bass)- When in doubt, reduce.
"Falling Apart" by BSM (Guitar)- This song seems like a fun party tune! Unfortunately, I need to PT another song by this author, because apparently I already did one for this song when I was trying to upload "Steven Wells" the first time around. This was back when the Creators site was still buggy from the RB2 -> RB3 transition.
"Feast Or Famine" by Within The Ruins (Vocals)- This one was easy, being all talkies. I made a second pass through just to make sure they were time right.
"Lift" by Poets Of The Fall (Guitar)- I love the song, and despite it's length (I have the GH5 guitar, so I can't fast forward) it's a beauty to listen to and is mixed well. To listen to.
In Rock Band, the main guitar part definitely needs to be louder if you're trading off between two guitar parts. For an exmaple of how this is handled well, check out "Reptilia" by The Strokes.