Great article, thank you for sharing. A lot of good games in the list. I don't know if they can all be called under appreciated, I think that some of them are very well know. I totally agree about Qwak, such a polished single-screen platformer with a perfect difficulty curve that many people don't seem to know about.
I would definitely add Highway Hawks to that list, as well as some adventure games such as Kult: The Temple of Flying Saucers and Innocent Until Caught.