Colour eink will never look much better than colour on newsprint. It all has to do with contrast and brightness range. The best brightness range that can be achieved is about 60 to 1 and that would be on a very good, white, high gloss stock (think of a glossy black and white print). a range of 60 to 1 corresponds to a optical reflection density of about 1.7 which is very difficult to create. I doubt if the best of the current eink screens manage a 10 to 1 brightness ratio (this would be an optical density of 1.0) and if these screens rely on reflected light, they will should also use a subtractive (yellow, magenta, cyan) which may make the contrast problem even worse. It's simple physics (and chemistry ) folks. These is nothing that reflects 100% of the light or absorbs 100%. No eink display will have bold, bright colours. By way of comparison, a colour transparency can have brightness range of up to about 300 to one (an optical density of about 2.5). A back-lit lcd panel (or a crt) can easily get 1000:1 (equivalent to an optical density of 3).
So if you are hoping for eink with colours like a high quality magazine, printed on ulta white, high gloss stock -- forget it, it simply can not be done. If you would be happy with colour as it appears in newspapers, printed on plain white (sort of) newsprint then you will be happy with colour eink.
If colour eink screens can be made with no worse than the current brightness range and at least the same resolution (I would like more than the current 167dpi) then I would be quite happy with them. I don't expect good colour reproduction in most of my books and if good colour reproduction is important then an eink reader would be the wrong device to look at it with.
But for general purpose use, text books, maps and such, a colour eink device would be great.