My first game on this platform (HTML5, CSS, Javascript) was only about 3MB, and that was mainly because I had WAV files for music; I probably could have gotten under 1MB if I had used MP3 instead. My second game (also HTML5, CSS, Javascript) was under 1MB, with just my code, images, and some sound effects. A 3D first-person shooter called .kkrieger fits in around 96KB. It is vastly more impressive than either of my already-small games.
Unfortunately, gauging quality entirely off of file size doesn’t work well whatsoever.