There's too much syntactic sugar for my taste to the point it gets diabetic.

Callable classes really? For example you can write MyClass()();

Underscore to mark a variable or a function private, but you can still use an underscore to declare a variable inside a function so it muddles the comprehension. Are we going to lose some precious milliseconds if we have to write private in front of a variable?

There's also the need to use buildrunner for almost everything since the language wasn't thought out for modern use cases. It works, but this is very inelegant IMHO. When I peak at the generated code I don't feel fluent in Dart quite the opposite.

Then there's the ultra strict linter that won't let me add an empty new line where I want. The resulting code is very compact and is harder to read.