My big complaint is the number of titles that receive a Platinum rating on ProtonDB, in spite of technical issues. I have purchased more than one title with a Platinum rating that had significant issues running on my machine.
This is compounded that Steam/ProtonDB user reports typically have an abysmal level of detail to replicate a working configuration. Someone got it to run flawlessly, but there is so much wine configuration jargon that each time I need to dig into the issues, I waste time on something that otherwise would work on Windows. I would love if there was a 'share my Proton configuration' per game that could be made available to the community.