I think the view can be described as two axes: doesn’t work <-> works well, and is not fun <-> is fun. “It’s functional” is hardly a ringing endorsement, so let’s put it just above zero on the “works” axis.

It’s still “not fun” on the “fun” axis, so you’d expect the overall review to be negative as an average of “neutral” and “bad”. Yet, for some reason, OP is finding that these reviews weigh “it works” so heavily that the score is positive, not neutral or negative.

If anything, I would expect most people to weigh “fun” more strongly than “it works” (where “fun” means engaging, not necessarily “happy”)

Depends what you mean by “AI”.

Machine learning trained to find cancer can be (and AFAIK is) helpful in identifying early stages of cancer.

Hallucination machines, aka fancy autocorrect, aka LLMs, have no place in any setting where factual accuracy is of utmost importance, such as peoples’ health.

Would I be able to use the play store?

Yep! Most Android roms allow you to install a Google apps pack (“GApps”) on top of the system, so they’re installed as system apps like normal. There’s different packs, from the bare essentials (play store and play services) to basically everything made by google.

GrapheneOS is cool because it has a sandboxing layer, so you can install those same Google apps as normal user apps and avoid giving them the extra permissions they get as system apps.

What about my bank’s app, or something that uses location, like Grindr?

This depends. Google’s Play Integrity API is used by a bunch of apps to easily enforce “security” and disallow using the app if the integrity check fails. Thing is, the things it checks for aren’t necessarily what’s secure, but more like what does Google approve of. For example, I would consider GrapheneOS at least as secure as official Google Android, but it can fail the Integrity API checks.

My bank apps work fine, but that doesn’t mean yours will. And I don’t use dating apps, so no clue there. Really, you’ld just have to try it and see how well it works. Just be sure you have good backups if you do, and also know how to restore the original system if using an alternate doesn’t work out.