Apart from the e-ink, the best thing about the Kindle (for me) is that you can email documents to it as an attachment (Word document, HTML, plain text, whatever) and a few seconds later the document appears on your Kindle, formatted and ready to read. The Kindle server converts the document to Kindle format on the fly.
It makes it very easy to use the Kindle to read any long documents. And of course other people can email documents to your Kindle too (hence the value of services such as Instapaper).