Contrary to others, probably due to the fact that I worked on a real-time trading Swing application, I consider Java to be the best answer to your requirements (however, i consider this question as subjective, as previous answers already shows). Let me develop.
It must be easy to install (run-time is a drawback, but C++ wrapper and/or installer can solve the issue I think).
Using Java, you can rely upon Java Web Start, which is, as far as i know, the best solution for easy to use applications : you click a link on the browser, and the application is installed in start menu/desktop and started as soon as it is downloaded. Seems like Adobe AIR offers an equivalent feature, but to my mind Java Web Start integrates, due to the deepness of its ecosystem, far more powerfull distribution solutions (like, as an example, the easy ability to generate the .jnlp file on demand).
It must be fast and have a rich GUI (not 3D game, but definitely some 2D graphics).
Contrary to most popular belief, generating good graphics in Java is possible. Take as an example a look at excellent filthy rich clients companion site of the excellent book.
The development environment must be easy to establish and the UI development tool must have drag&drop functionality to define application layout.
Eclipse is a defacto industry standard for IDEs, and it integrate multiple DnD IDE builders. I would simply take as example the recently liberated Windows Builder Pro.
Target application must have native look and feel. The professional paid support should be available.
Well, Swing default look'n'feel is indeed a little different from system one. however, there are excellent third-party ones, listed here, as an example.
Finally, some examples :
- the excellent Palantir Technologies blog list some outstanding Swing applications
- Gephi is a rather complete and efficient high-volume graph viewer
- My previous work (don't consider it as a masked ad, it's only a way to show some rather solid Swing).
