I'm a design buff, largely because design incentivizes play. When design starts to distort incentives, I dislike that design. Expertise distorts incentives by being so attractive in the all-or-nothing skill arena. When it's a do or don't roll that can have big consequences (not seeing an ambush, tracking successfully, hiding from all the sentries, etc.) then the availability of such a distorting mechanic twists the incentives of play. For example, I have a ranger character in my current game and their player has dipped rogue just for expertise and the bonus action options because both of these things mean they can be a better wilderness warrior. That's just weird that it's the rogues who can be better at any skill than even the "smart" class and that rogues just run faster, every turn, than anyone else (high level monks excluded). If your concept has an aspect to be really good at a certain skill, then rogue (or bard) becomes highly incentivized regardless of the other aspects of your concept. Same with being fast -- rogue has abilities that strangely result in being able to run faster than anyone else. That kind of distorting pressure annoys me. I can easily deal with it in game -- rogues just do these things. But, from a design perspective, expertise shattered bounded accuracy, which is an annoying design choice, especially when the concept is already better done by both the advantage and the reliable skill rules. Expertise is just number inflation, and that's boring design especially in a system whose design goals include tamping down number inflation.
So, in play, whatever, I deal the game is fun and we all have a good time. When I put on my design hat, I hates expertise because it doesn't fit.