Everyone else has mentioned the preformance problems, but my point of contention's gotta be the reactivity of everything.
every girl exists in a bubble for lack of a better term: there's no relationship between them at all, it's them and you. it's not a harem situation, it's 3 separate monogamous relationships happening at the same time.
If you get certain stats up, the girls will go off and fuck each other in some random out-of-the-way spot, but this has literally 0 ramifications on anything which feels really, really weird. it happens, but you can't interact with them while it's happening and they won't react to your presence , care you saw, or have any dialogue relating to it even though it's the only real interaction they'll ever have with eachother outside standing still doing canned animations while muttering "is that so?" to each other.
it's been this way with illusion's more sandbox-types for a while and i'm naive to hope otherwise at this point, but AA2 is ancient at this point and wasn't even that complicated behind the curtains in terms of how it all functioned; the fact it's still the best-in-class at what it does a decade later confounds me.