I don’t think there’s consensus around very large things, but there are some regrets that are commonly expressed about smaller stuff. For example, lots of people think the PartialEq/Eq split was a mistake. I like to half-joke that String should have been StrBuf. Macros have several flaws and are under-developed, etc.

There are also some thoughts about Rust-like languages with some differences, see https://boats.gitlab.io/blog/post/notes-on-a-smaller-rust/ as a prominent example.