Making Javascript a first-class citizen can't be understated. Before V8 came along, Javascript was good for doing form validations and not a lot more. Chrome sparked a Javascript engine arms race that has tremendously benefited web developers and users.
That's nice and everything except now they want to kill it and replace it with Dart. Basically Google hated Javascript (and rightfully so) but used it to gain market share, and now they can't really get rid of it. To add insult to injury, now you also have server-side Javascript.
