It's really hard to give a review of an email service. It sends mail, it receives mail, and the user interface is pretty enough for what it needs to do.
It's a bit cheaper than a comparable service from Google Workspace, and it encrypts emails when it's possible to do so, which is nice.
An extra plus is that it allows you to use your domain as an alternate email, both for receiving and sending. So if you don't like @proton.me, you can replace it with a domain that you own.
A minus is that you need to install a bridge to use standard SMTP clients like Thunderbird.
All in all, I'm happy, and I'll continue to use it.