In my personal opinion:
It is fast to work with and not that difficult to learn
Easy to explain to "non"-developers
Increasing supporting community
Integrates more and more with SAP
Project based approach on the project dashboard site works really nice, Especially the stories.
But, the downsides (for now):
Expensive (regarding SAP Cloud Foundry I have to add resources regarding users + postgresql + appl serv on Cloud Foundry. Currently very expensive at SAP.
Not aimed at the smaller companies although I think that this should be your next focus point in the next couple of years.
Hope this helps!
I don't have a background in IT and I found it quite easy to learn the basics of Mendix (of course I am still learning, but the basics came pretty quickly).
What I like the most is the visual representation of logic in microflows and xpaths. Simply go to your domain model, follow associations to where you need something and write it in your xpaths :) also like how you can see which options are available for use in your logic.
I still have difficulty figuring out how to use REST services effectively and read those made by others, but I haven't tried REST in the newer mendix versions yet.