Dictionary was one of the important features for me as well. Although I never used K1, the ability to look up a specific word as opposed to the entire line and viewing the definition without leaving the content is perhaps the best implementation I've seen in all the ebook readers I've researched.
To top that off, it sounds like you can lookup Wikipedia content through Whispernet, meaning anytime anywhere!
Pointing to the word with a stylus like iRex DR1000S would perhaps be even better, but iRex has no support for highlighting and annotating of mobi books at this point and adding stylus support means embedding a Wacom tablet under the screen and significantly adding to the cost of the device. Sony had a chance with it's newest touch-screen PRS-700 reader but they have no dictionary support and the new screen does not display text as sharp as other eInk readers. Bookeen Cybook Gen3 has a very similar joystick driven dictionary lookup support, but K2 adds a keyboard for annotating, access to Amazon content, and Whispernet for Wikipedia searches. You just can't beat the Kindle!