We just released this over the weekend, it was built from a very similar mindset - Cloud9 looks great but not 'open' enough. If you like it, pass it along: http://www.wiode.com
Coloring some keywords might make things look pretty, but it surely doesn't make it all by itself an IDE or even a good text editor. Line numbering isn't a 'feature', that's a basic necessity. If these things are taught as 'features', what else is a 'feature' then? The ability to save the text without errors? Let's raise the bar here, please.
For me, Eclipse or VisualStudio is an IDE. Aptana (now Appcelerator Studio) is also more than just an editor. TextMate, VIM, Notepad++, UltraEdit and the like are not IDEs. They are (mostly dumb) text editors.
Personally I draw the line at whether there's contextual code-completion provided via instant introspection or background compilation.