i've now played through a lot of the new game (since yeah, as said above, it is more just a second game than an update), and it's... something! it seems like it's sort of a remake of one of the other MucchiMucchi games, though with some stat mechanics and sort of "alternate futures" for the main girl.
it's a fun concept, but i find that it mostly just means it's kind of the worst parts of the franchise (talking to a lot of people for a long time with weird requirements to eventually get scenes) with a lot more downtime than the main game here. i really like the alternate futures idea, but even once i discovered the secret room (find all 10 coins, give them all to your grandmother, and there's a room which lets you get infinite items to boost/decrease stats) it still took a while to go down whatever path i wanted
i don't think i've seen every scene, but i couldn't find a gallery to confirm nor deny this, and the majority of scenes this game had felt like some of the worse ones from the main game? mostly from a personal preference point of view; a lot of them are just kind of "the main girl has sex", without any of the interesting bits of the concept (i.e., exploiting her lack of knowledge to have something lewd happen, like make her do jumping jacks or move her top), leaving this as just being a "pedophilia for sport" type of game--since if you're not trying to enjoy those parts of it, and are just looking for the regular "has sex" scenes, with this girl whose body is like an adult but her mind is like a child, that feels kind of like being attracted to the idea of a child
not to call anyone here a pedo or anything ofc; that's just kind of my issue with the series as a whole, which i deal with by enjoying the other kinds of scenes
overall, this sidegame is a fun concept, but it's a pain in the ass to get to the various scenes, and (in my opinion) the scenes aren't that worth it. it was really fun to see the 3(? that's how many i found at least) alternate versions of the main girl, though!