Speaking of input, one thing that I feel basically all games get wrong is: Requiring window focus to process mouse input.
Try focusing another window, then bring the mouse over Twitter. It just works.
With a game, you'll first have to click, and that click may or may not be handled. You're may miss the mousedown event, and only get the mouse up event.
And before you click it won't listen to mouse move events. So it will seem like clicking on a button won't change anything, or it will seem like clicking won't move your character, but it will, to a place you weren't intending to.
Overall it will just feel janky more than anything.
Just handle it like a regular program would. That's the trick.