I'm excited about the recent work on CSS (particular Houdini). I haven't felt like this since I got a book of IE 5.5 features. Don't get me wrong -- CSS has gotten a lot of new features over the last 14 years, but they've been like basic things you kind of expect in a style framework, like new layout options or variables.
But IE devs were unhinged. You could build JS code as a module and attach it to elements using CSS.
Finally we're getting those kind of unhinged features again.