Can you name another very popular and very good looking Swing application?

Even if you can, you can count them on one hand. Swing was a massive failure, and rightfully so, because Swing/JavaFX apps look, and more importantly, feel, like a broken mess.

In contrast, SWT/JFace apps look a lot more native and feel extremely snappy. Apps build on the Eclipse RCP are in general pretty decent looking and they enable all the native controls and functionalities of the host platform.

Jetbrains IDEs could almost have an NCurses GUI, and they would be worth using. How pretty they are is mostly orthogonal.