This is one that I admit is fairly subjective, and I apologize in advance if this is not scientific enough, but: it just feels right.

I think they optimized the way code drawing is done in such a way that it just happens with the least amount of time possible between typing and drawing. The end result is the same as if you typed anywhere else, but because the response is cut by, say, 16ms, it just feels fast. I remember the first time I tried VSC - I almost felt like the letters where coming out from under the cursor ahead of time! It was a weird moment.

The counterpoint is IntelliJ. It's not a slow IDE (I used Eclipse before so that'd be unfair to say), but maybe it has a couple of frames too many before drawing what's typed, so it feels like it's lagging in comparison. Maybe why they're making it a point of future releases[1] to reduce any typing lag.

[1] http://blog.jetbrains.com/idea/2015/08/experimental-zero-lat...