'Look and Feel' was a key feature from the early days of Apple's first Macintosh OS, and has lasted within the DNA of windows systems to this day.  It has shaded the design of application user interfaces for the last 30 years.

The Look and Feel of a platform defines a set of rules for User Interface developers to follow.  The rules are laid down by the platform vendor, and typically cover colours, shapes, layout, and typefaces (the 'look'), as well as the behaviour of interactive elements such as buttons, boxes, and menus (the 'feel').   And each application follows them.   So these guidelines become an essential part of the platform.  The benefit to the user is a consistent way of working for every app: users don't need to learn how navigation and interaction works with each new app they download or use.  They get an aesthetically pleasing experience.  Altogether they get a nice world.

So a key feature of all of the platforms: Apple IOs, MS Windows, OS X, Windows Phone, BlackBerry, Android, is a large and complicated set of rules about user interaction.  In many cases, especially with Google and Apple, apps that do not conform risk being rejected by the vetting process and not being allowed distribution. 

Why are things changing?

One problem about conforming to Look and Feel is that cross platform apps become very difficult to produce.  If the interaction is different for each platform, then you need to write that interaction many times.  So, even if you've found a way of writing code that's completely portable across all your target platforms, you still have the job of making it work very differently across the different platforms.  You have to follow the skinning rules to make the colours conform to the user's chosen colour scheme.  You have to conform to the platform's accessibility rules (support for disability).  You have to conform to different ways of navigation through the app: Android relies heavily on the back button; iOS has a hierarchy, with 'up' buttons (one might speculate that this follows the culture of the organisations that created them!).

With financial and account management apps, we're really sensitive to the cost of providing for all these different platforms.  In many cases the advantage of an installed app over a mobile-friendly browser-based page is only marginal, and multiplying the development cost by two or four makes the economics of an app prohibitive.

So it's a relief that recently we've been noticing that the heavy hand of Look and Feel has become much less important.  There are many apps that behave and look almost unchanged on all their platforms.   This is not particularly true of the major apps, such as Facebook or Kindle, where the marginal cost of rewriting for each platform is small compared with the total revenue from the app.  But it is common with utility and marketing-style apps.

Several trends have contributed to making this more acceptable to users.  The first is the rise of web apps.  Users are accustomed to interacting in their web browsers in a rather different way from they do with their apps; so given the large number of different kinds of web app, they are already dealing with many different Look and Feels on their device.  A second trend is the branding requirements of the major brands: Apple and Google have their branding requirements, but so do Facebook and Amazon, for example.  Facebook and Amazon want their apps to conform exactly to their brand colours and images, and they're sufficiently powerful that it's not worth the platform vendors fighting this.  So the idea of a platform 'skin', which was essential to the early platform Look and Feel guides, has now been abandoned.  A third trend is changes in the Look and Feel guidelines; not every app gets back engineered to support these changes, so users become accustomed to using apps with both legacy and current 'Look and Feels’.  And a last and very significant trend is 'gamification':  games have always tended to make their own Look and Feel, mainly because the original platform Look and Feels were designed for apps using forms and menus, and forms are not really important in the design of games.  So mobile games have rarely followed Look and Feel guidelines, and the policing of Look and Feel normally just accepted that.  But 'gamification' has meant that the rules for games now apply to every app.  So much for Look and Feel!

The new mantra: usability

In this new world where Look and Feel is much less important, one thing does dominate: usability.  It is widely accepted that usability is the main attribute that causes apps to succeed or fail.  Thus whether an app follows the platform guidelines is important only in as much as it improves its usability. 

So which aspects of Look and Feel are important for usability in apps?  We can identify a couple:

The main one is navigation.  Because of the small screen size, there's no space for navigation instructions on the screen.  Instead there are conventions that users must learn in order to navigate apps. So, for example, an Android user learns to use the 'back' key to return to the previous screen; an iOS user learns to use an arrow in the top left hand corner to return 'upwards'.  Similarly, but slightly less important, an Android user expects to see tabs with text at the top of the screen; and an iOS user expects them at the bottom with icons.   This article by Google provides a good set of guidelines on which navigation aspects of Look and Feel matter most.

Another important item is actions.  Android, iOS and OS X expect actions based on screen controls (sliders, check boxes, etc) to take effect immediately after they're changed.  So if I click a check box titled 'Wifi on', the wifi turns on immediately.  This is different from the MS Windows and Windows Phone Look and Feel where the activities do not happen until the user clicks an OK or confirm button.  It's particularly important not to do as some early Samsung apps did, and use the Windows-style interaction on an Android phone. 

Other than that, do as you please, so long as it's very usable!

This makes cross platform apps much easier to develop.  The platform Look and Feel is reduced to a few key elements of navigation.  For everything else the decisions must be based on the benchmarks of user experience:  Is it pleasing?  Does it require the minimum amount of user thought and effort to achieve?  And most of all, is it fun?

Beautiful, easy, and fun are the criteria for a successful app.

Charles

Thank you to Rupert Whitehead of Google for pointing me at the links on usability, and to Penrillian's Chris Allison for guiding me through the intricacies of Mac picture editing.