It seems to be a common thing that these headphones don't fit people's ears properly, and fall out. This is certainly the case for me. I used to own a set of Koss PortaPro's, but those eventually broke and I had lost the warranty. I decided to buy these as a replacement. Now, I have seen a couple of reviews describing the sound as "tinny" or lacking in bass. This is certainly not the case, if they fit your ears correctly. If you are to push them right in so that they seal off the sound, the bass is dramatically intensified. However, they (at least in my case) seem to slip out of that optimum position quickly and lose this powerful tone, and suddenly let in sound from outside. Yes, I have tried using both sizes of ear plugs provided, but neither seem to stay in my ear and seal the sound.
Overall, the headphones themselves provide a brilliant punchy and crisp tone... if they stay in your ear.