Keeping extremely busy
Yes, I said new theory. Not new as in "OMG, nobody has ever seen this before", but new as in I hadn't used certain chord progressions with 8ths and 6ths together in that manner before. I'm certainly enjoying the different approach to things.
Probably the toughest part, though, is the shared solos. Moving one guy from lead to rhythm without missing a beat on the rhythm or the lead is tricky to say the least. Again, I'm up for the challenge, but it's certainly something I haven't tried in the past.
I guess what I'm saying is that I'm intrigued by every tune I play and look forward to what I can learn in the next song on the album... and then the next album... and the next... playing with a purpose is good.