I must be missing something with this game. It seems like a lot of mindless clicking and grinding for what amounts to access to a scene viewer. I'm not seeing much point after unlocking all the positions with one character.
It's not that big of a sandbox. The fun comes from traits and modules (think custom AI and effect scripting) that have effects on relationship stats, then further fun comes from weird modules with functions that range from alternative ways for characters to be "killed", body and clothing transformations, interesting stat changes, etc.
There's more depth with the game with the stuff I mentioned above added to it, though it is shallow as a sandbox to the degree the shallowness is felt slightly even after enhancement via mods and behavior modules. However you can't really find much better for a hentai game.
I thought about finding similar fun in other games before.
A good way to compare this game to the most similar triple A content I can think of: treat it like The Sims (3 or 4) with more speed between character interactions and opinion changes, the possibility of fights and murder, and with a heavy focus on just the social aspect instead of the random pop-up dream / goal / motivation / aspiration aspect where your current sandbox goal (for yourself made by you) is derailed through heavy incentivization by the game giving you whatever mission it thinks is appropriate for you.
AA2 is the unfinished dream experience that Koikatsu could have been if it moved in the direction to improve the interactive aspects instead of forsake them entirely. In an alternative universe where Koikatsu was instead a direct improved successor to Artificial Academy, all of the expanded voice acting variety would actually be significant to character development, more actions would be available to the player for friendship and mayhem, and all the graphical excellence from Koikatsu / Honey Select could be used with a richer foundation of gameplay.
Alas, even when considering games like Hentai High School Plus, or modded game builds for the Sims, Skyrim, Honey Select, Koikatsu, they don't quite give the same chaotic social feel. The only game experience I've seen that comes close to AA2 and in a sense surpasses it is highly modded Rimworld. Really. A lot of modding goes into that result and 2D isometric characters is not a good medium for porn scenes but character and world building happens with good weight on both letting the player do stuff and having the game give you a good fight for your effort, and with LoversLab RimJobWorld and some choice visual replacement it does a fine job if a bit uglier.