I don't think a Java applet is not anymore a very good approach. I've once programmed a pretty good Java applet viewer in combination with a PHP based Conquest webserver but finally I gave up 'cause of all the modern browser restrictions. I think HTML5/Javascript will do it in the coming.years just like the DHV project.
At this moment I'm working on a Cornerstone project based viewer which is looking awesome to me in many details. See https://github.com/chafey/cornerstone. This project seems to be in full development.