I think of Dart as being C#-lite, although the latest changes with class modifiers have somewhat complicated the sentiment. For reference, my background is in OOP/JavaScript land, with patches of Scheme, Rust, and way more Go than I ever wanted. I really think Dart is one of my favorite languages, it’s just a joy to work in. Clean, fast enough, and to my experience so far, footgun free. I also know @munificent here is a principal developer of the language, and he’s done a good job. (But in case he’s listening, please add Rusts discriminated enums, it really hurts to move from a language with them to a language without them.)
As for Flutter, as a WinForms and UWP developer, coming to terms with its Dart-declared UIs was tricky, especially when coupled with the constraints based layout system. But I’ve long since crossed the threshold in my mind, and now I can strongly say I don’t want to program UIs in anything else again.
The one real complaint I can agree with is that the ecosystem kind of sucks, but it’s growing and getting better. I’ve seen some profound growth in the area over the last two years.