1) It work.
2) The displays look good.
3) It's easy to use.
4) It's fun to work with.
5) It does the job!
Looking forward to the next update.
It assumes a good knowledge of underlying technologies. I can see I need to bone up on advanced CSS and get my head around patTemplate. Not unreasonable expectations for anyone claiming to develop advanced interface features, such as this enables.
How about a field on this site for "Required knowledge/skills"? Here's what I'd put for ExtMenu:
Required knowledge: Advanced CSS, patTemplate, mod_mainmenu functions