I've seen the show twice - the second time for a few reasons:
1. Yes, the lyrics are hard to understand. Plus, she writes kind of random stuff, so it's hard for your brain to decipher what maybe it should be. I went home, listened to the album. I also realized that 1/3 the music is from NOT Jagged Little Pill. So, I found using the song list, and pre-listening reallll helped for my 2nd visit.
2. The observation that this is Next to Normal and American Idiot combined is SPOT ON. I couldn't have said it any better... and i had been trying.
3. If you love her music and know it by heart, some of the handling of lyrics, moving lines around, how the song sits in the show, for example, could annoy you. I had a super fan with me and when Unsexy happened, he just groaned that it was ruined. He would note to me where verses were switched or edited. BUT, he was really glad to have seen the show and we then listened to the JLP CD like 100 times for 2 weeks.
So, those are just my observations, but they do fall in line with what a lot are saying.
I rushed both times, so $40 to see this show is a very good deal. I had a rocking good time (once I knew the songs/lyrics better).