I have a fairly basic MP3 player which is only let down by the quality of the earphones. For quite some time I've been using better quality earphones, but these Panasonics are an absolute revelation!
The sound is crisp and clear across the full range, with wonderfully rich bass tones. As mentioned elsewhere, the "Ergo Ear Fit" buds are superbly designed so are a snug, comfortable fit, and don't have the all-too common tendency to pop out when exercising. They also block out unwanted external noises, so do everything I'd expect from a pair of earphones.
For the price, they're an absolute bargain.