Aside from the many technical innovations, that we’re learning about, theres the people involved and behind it:
Daniel, and team–extremely capable, experienced and they care about user input and have the chops to implement whats needed and wanted.
Steinberg/Yamaha–who believed in the team and project so much they financed it, after hiring everyone when they were fired by AVID.
Many-including myself–think the BIGGEST and BEST selling point of Dorico, and what it has over Sib and everything else, are these people 
Thanks Bob
Tha best thing to do is read the Making Notes blog, written by Daniel. It charts the development history of Dorico and many of the key concepts and features of the programme. http://blog.steinberg.net/
In addition to the people behind it, I think one of the biggest things Dorico has over the alternative notation options is the modern code architecture. The basic fact that Dorico will not be slogged down by having to support 25 year old legacy code is a huge plus for the program. There will be several disadvantages to using Dorico at release (without chord symbols, it won’t even be able to do a simple lead sheet) but I’m very hopeful that without having to worry about all the legacy support issues that Finale and Sibelius have, that the developers will soon have a complete and robust program that can surpass the abilities of the other two.