I thought the singing was excellent in Yuki's set, with good intonation and ensemble. Joelle did a great Emily impression. Joelle and Kaori kept switching off on high and low parts. They also looked like they were having fun. I was way off to the side so I got a good view of Kaori, and she has a great attitude, like a fun-loving college student. Yuriko also looked slightly more animated than usual I thought. Joelle still seems to me like she's settling in up there with the other singers. She definitely has different dance moves than Yuki's singers usually do. (But Keiko and Wakana, please come back!!!!)
I wasn't very impressed with May'n's singing but she really got into her performance. Her face on the big video screen was so intense and emotional at times, it looked like she was crying. May'n used some of Yuki's band, along with her own keyboardist and some male dancers. (I couldn't tell if her bassist was Jr. He sort of looked like him but he wasn't wearing his trademark glasses so I wasn't totally sure.) I liked Sayuri a little better, but she's not really my cup of tea either. As Westkana mentioned, she sang the song from Boku during her set. She played acoustic guitar and had a live keyboardist with her, along with recorded backing tracks. I really liked the animated videos she was showing during her songs. I don't know if it's from an anime or if it's her own personal theme. I noticed that one of the characters in the videos had the same outfit and hair as Sayuri.
Aimer was doing her piano acoustic versions during her whole set, so it was really nice to hear Yuki's full band accompanying her for Hana no Uta. I have to say, other than that one song, I'm no Aimer fan, but she really impressed me during this concert. When Aimer came on and started singing following Sayuri and May'n, I thought the overall level of musicianship just shot up several notches. Even though I don't really like her voice, she's a very expressive singer with good control, and just on another level from May'n and Sayuri. I didn't realize that she was still doing her thing of not showing her face. It was very obvious that she didn't want to be seen on the video screens. Also, she probably spoke English the best out of all the singers, although Yuki's English is good too. I didn't realize that Aimer is pronounced "M.A." like in French. I always pronounced her name to rhyme with "gamer." Maybe that's why people looked at me funny.
On another topic, I noticed on Twitter that Yuki, Yuriko, and crew were chowing down on a lot of Pink's, In N Out, and Ruby's during their LA trip. I wouldn't have advised that, because you don't want to risk jeopardizing your first US show in several years due to a digestive emergency.