I am always motivated by achievement systems. Humans generally have an urge to complete things and achievement systems just use that fact to get them involved. And as a roguelike player I like the permadeath feature - of course!
Implementing sound effects in JavaScript is a little special, but not too complicated if you know how to do it. Just check the source-code of RunToTheStairs from its GitHub-page to see how I have done it. The sound-effects are all loaded as HTML-elements. Just look for the <audio>-tags in "index.html". Let us take the nitro-sound as an example, it is played by the following command:
document.getElementById('soundNitro').play();
It can be found in the file "player.js".