Personally I find it embarrassing that we use a device with gigabytes of RAM and millions of pixels to emulate a 19-button device from half a century ago.
It's probably hard to come up with a better interface. A pocket calculator can be operated with very little cognitive load. It's easy to memorize because things don't move and it's easy to discover because ~every action is always visible.
It's also good enough. Most people don't need more than a pocket calculator. Sometimes I use WolframAlpha, very modern, but I type my query on a keyboard whose design predates the calculator (QUERTY in <1873 vs "10-key" calculator in 1902)
I like to use a REPL (like MATLAB or Python) where I can enter expressions with a real keyboard instead of hunting and pecking the skeumorphic calculator GUI. This also allows me to see the history of my calculations without resorting to the weird mirrored calculator. Even something like a TI-85 graphing calculator offers this.
