Really enjoyed it. It was easy to understand and I liked a majority of the dialog. I'm not a huge fan of how the 4th girl's story begins but the ending was nice and satisfying. I did like that it has a sort of ending and epilogue at the moment, but I definitely would like to see them all grow even bigger even if it isn't canon. The overseer is my favorite, for multiple and obvious reasons.
For the gameplay, I felt it was a lot easier than expected, with only a single level requiring some "grinding" (3rd girl, stage 3) because I just didn't have enough Match Power at the time, but I only spent like 5 minutes longer than I should have trying to get as much credits so it wasn't a problem. I think the later stages honestly had too much RNG with getting the right colors. Near the end I was just refreshing so I could meet the color requirement every level. Before that, however, I had a lot of fun.
I'm not sure if there are any other upgrades you can add; 30 seconds is just enough time to keep it fun and challenging while leaving RNG "fair," but you also can't limit the amount of refreshes without it becoming too frustrating at the end. Maybe a "super gem" option where getting a pair of 5 eats a row or column; that will be hard to balance though.
You could also implement a hard mode where you limit how many Match Power upgrades you can get based on how far you level up the girls; it'll get really rng heavy at the end, but its for a challenge