Wow. I just finished Episode 7 as of writing this review- and let me say, the music is AMAZING!! The 'Girls Talk' (ending song) is so well done and I actually listen to it sometimes when I'm bored and have nothing to do. Love all of their voices and the voice acting is done pretty well.
The chibi art style was so adorable and I loved the cast of Re:Zero's designs! They were so cute in the art style of the anime.
I haven't seen any of the animes featured in this collaboration... but I do know a little bit about each of the characters. I know for certain that if you are not like me, and have seen all of these animes, then I'm sure you will enjoy this collaboration!