Good question! There's no single thing, I think, and the things I dislike about it aren't even really technical criticism or the like. They're more... aesthetic? I find the syntax unpleasant, for instance. It's extremely opinionated and a few of those opinions are ones I disagree with.

Also, just generally, it tends to make even simple things pretty complex. I understand why and am not really objecting to that, but it does make using it a bit like running with lead shoes.

I expect that the latter part may get better as I use it more (but perhaps not -- there are other languages I'm fully competent in but dislike for similar reasons).