Just a few interesting notes about controllers from recent playtesting:

1. People will continue to attempt to use the first controller that works with your game, even if it is no longer functioning. It is very important, therefore, not to switch from the keyboard to a mouse, or from a mouse to a console controller, etc. Keep the player using one controller from start to finish.
2. Players don’t necessarily explore to find out whether there are controls available beyond those they are aware of. They might push all the buttons on a controller, but that’s about it–and if a button doesn’t have a function at that moment, they probably won’t come back to it later. Don’t assume that the player will learn all of a game’s controls without instruction/tutorials/etc.
3. Players will do things as fast as they can, not as fast as they need to. If you want players to do things slowly–e.g., in a rhythm game–you need to incentivize the pace you’re looking for, or find some other way (for example, visual and sound design) to lull them into a more restful pace.