I first started playing Idolmaster Cinderella Girls: Starlight Stage (or Deresute for short!) in late 2020. In early 2021, I deleted the game and started playing again later that year.
Just to make things clear, I am only familiar with Deresute. I tried playing Shiny Colors but the gameplay didn't suit me. With that being said, Deresute is my favorite game out of the IMAS franchise and one of my favorite games in general!
I love that there are many, many characters! It may be a little overwhelming at first, but there is an idol for any kind of player! I love the variety and the music in the game is so catchy. I also really love the card art and costumes, it's so pleasing to the eyes! I would love to cosplay one of my favorite cards... maybe one day! I'm not super active in the fanbase, but I do know that IMAS fans in general tend to have a bad reputation based on how they treat some of the characters... please note that I am not one of those people! >_<
That's all I have to say about the game itself! It has soft spot in my heart and is definitely one of my go-to rhythm/mobile games. Sometimes I will take breaks from it, but I always find myself coming back to it! You can download the game on iOS by making a japanes iTunes account and downloading it on Japanese App Store! Check it out! But keep in mind that the game is completley in Japanese. There are tons of helpful tutorials online though!