Too often, when someone or a company is planning on coming up with a new app, they will wonder what's the best features or best way to design it, but the most common problem should be solved before these.
That is, how is the function of it different?
The features, user interface (UI) comes second to the user experience (UX). The user experience being, what function(s) does the app offer. Does it offer better insights to something, does it bring better information to the user?
UX: What functions are being offered?
UI: What does the interface look like?
For example, someone may want to offer an app to count calories. However, you can change the UI on the app and it appears to be better or different, but in fact the UX is relatively the same.
If you don't solve the UX problem first, then the app is more likely to be doomed.
If you don't have a solid difference in the function of the app, then it's much harder to get a good user base and all UI investment will be lost.
However, UI is still important, because if the information that appears on the app is too complex but offers great function - detailed insights to problems, then UI needs to be solved.
For example, if you are in a complex environment, like medicine, you want to focus on UI more because a better UI will limit the number of problems a user is likely to make. Too much information may take too long to asses in a fast paced environment, so the user, medical professionals, want very good information (UX), but they want it in a simple format.
A simple way to explain the difference between UI and UX is a blog. The UI of a blog is pretty similar from site to site - nice pictures, content and a sidebar. However, the UX, the function of the blog, could be explained by the content provided.
With today's day and age, most apps are getting more efficient, too streamlined, creating instant gratification. There is lower decision making and greater impulsivity. The market place is competing for user's attention. Should we add complexity to our designs?
With Google creating big pop-overs that take half the page, to create stronger call for attention, this concern is something that needs to be addressed as consumers are getting "lazier". Are we creating a lazy society?
One aspect to consider is a slight variation in design to create complexity. Stronger design, something that creates more interest rather than less fatigue.
I think both of these concepts work, simplicity creates more attraction as it is simpler, cleaner and calls more attention to one or two things, whereas complexity can create interest as there is more.
One problem that I've run into in designing ME Keys is that I created a solution that was too simple, there wasn't enough complexity to it. For design to be effective, there needs to be an element of complexity to draw interest. If it is too simple, it seems less interesting.
However, simplicity creates a big draw, because of low decision fatigue, which is good for a call to action. Afterwards, when you have customer interest, complexity can be added to create curiosity. Curiosity is the cornerstone of motivation. When curiosity is gone, interest fades.
So, the issue really is, how to get and keep consumers, you will need to apply both simplicity and complexity to your design. Too complex and they will be frustrated, too simple and they will be bored.