I closed my Apple Card a month ago. I think the biggest part I miss is the ease of making payments, since they post immediately when paid from Apple Cash. Lots of people say the Wallet integration is its strength. I closed mine because of the Wallet app. I would get issues where searching for transactions and tapping 'see all' would crash the app, transactions would be pending in perpetuity (like something that I bought two years ago and paid the full balance of at the time) and it was frustrating. Even if bank apps seem clunky, at least they're accurate. Apple Card doesn't put the money part first in my opinion, and when it comes to money, you need better control and information.
I'm currently in the midst of talking with Goldman Sachs because Apple refunded something to my card after I closed it, but that's not necessarily the fault of the card, rather being unable to change refund method with online returns.