I'll just comment on the vocal tracks and whether I added them to my YK playlist or not:
-Remi-
shadows and fog - As much as I love Remi, I really think Kajiura should permanently replace her with Joelle on future Princess Principal works. She's just such a better match for the jazzy music. This song also suffers from lack of FJ chorus, so not really a fan.
Rainbow ~Main Theme~ - This was superior to the previous live version in all aspects but one - the low operatic note at "amore carpita" that Remi didn't do this time. Am sad. It's my favorite part, so I'll stick to the old version.
petals and butterfly - I don't think this song should be performed with just a single vocalist. I liked Remi's singing, but I couldn't help feeling that something was missing, because clearly it was. The harmonies/layers of vocals really make this song for me, so I'll keep the album version on my playlist.
moon and shadow - It's an ok song but not top tier for me. This was better than the album version though, so replaced that one.
heigen - The last two songs were the highlight of the first album for me. Surprisingly I don't feel like this song needs harmonies. I think Remi did fine on her own and her voice fit the song better than FJ in my opinion. Replaced the album version.
a farewell song - This one was lovely too, personally I really liked Remi's take on this song. Kasahara already went full operatic on this one and I don't think Remi could've topped that so I feel like her semi-classical approach was perfect. I replaced the soundtrack version with this.
-Eri-
el cazador - Fierce parts: Eri > Yuuka. Gentle parts: Yuuka > Eri. Overall it's pretty much a tie. Sticking with Yuuka to 'cause I'm lazy.
voices silently sing - Was fine, but we already have a live version with Eri and FJ chorus, so I think this was just a downgrade.
moonflower - Not a fan. Kasahara was way better in this one.
hepatica - Never really cared for this song, the vocal melody is fine but other than that it just feels like nothing's happening.
I talk to the rain - Brilliant, instantly replaced the soundtrack version.
Credens Justitiam - No FJ chorus, no vocal bridge. Downgrade.
red rose - Eri was fine but what really sold me on this one were the instruments. Replaced the album version.
ring your song - Been done before, this time with no chorus. Meh.
That came across as way more negative than I expected. Overall I think it's an ok release, but personally I'm really disappointed in the setlists. With the solo vocalists they had a chance to do many never before performed songs but we mostly got either instrumentals or songs that have been done before either with the same singers or as FJ covers. Also, what happened with Remi's mezame? Did something go wrong during the performance or why wasn't it included?