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).
I share your sentiment about Rust. Fine language for sure, I just don't enjoy programming in it. Simply put, I don't like using the abstractions that the language encourages.
For what it is worth, I found pursuing Zig to be a breath of fresh air. It's a promising alternative in the same space as C (and also Cpp and Rust). Checkout Andrew Kelley's introduction to the language.
There are a few, and they aren't something that I can't live with, of course. A great example of the sorts of things I'm talking about are Rust's insistence on camel case and snake case.
