The interface makes CSS a joy to work with, especially when adapting someone elses CMS template! The eye dropper works a better than the other eye droppers I've seen. You get a magnifier so you can actually SEE what you're doing.
The expressions system is a great idea, but making color expressions isn't too intuitive. It would be better if there was some type of visual builder for this.
It's best for working on complicated CSS. For little stuff, a text editor should be file.