1) Types on the left
2) Statement, not expression, based
3) No privacy modifiers (aka, underscores everywhere)
4) required semicolons
5) no language support for json (de)serialization, or, json boilerplate everywhere (yikes)
I've tried to get into Flutter 3x now, and each time Dart has defeated me.
Flutter is quite good though, so take the good with the bad, I just can't stomach Dart (yet).