At first, the most important thing: buy only ORIGINAL Sennheiser, either from here, or from a shop. The original one has really good quality, and when you listen the music, you will not belive it. The fake one has bad sound. (I bought a fake AKG K324p from the e-bay, and I asked for replacement, they sent me another fake... I throwed them in the rubbish bin...) So after you buy the original one, you will be happy with it! I had Sennheiser CX 300 before, I used it for 2 years, but one day one of the speaker was broken. Than I decided, I have a look on the internet, to do some quality change. I was sure, I want another Sennheiser, because I tried a lots of earphones in my friends company, but no one reached the level of the CX 300's. I wanted only symmetrical cable, because the CX 300's asymmetrical cable wasn't comfortable, the cable was too long for the longer side. The CX 500 ist much comfortable with the symmetric cable, and with the new shape double-looking earplug. The volume control works absolutely perfectly from minimum to maximum (because it's original), and it cannot move from itself under the clothes... The volume is perfect, I have a Sony NWZ-S 515 mp3 player, the volume control is adjustable up to level 30, but I'm living in a big city, and when I walk in the centre, the volume level 20 is enough to listen the music loud, and to hear nothing from the environment noises. When I turn up the volume to level 30, the sound is still clear, and I feel myself in a club :-)
The difference after the CX-300 : a bit louder, more bass, more treble, and more high, the sound is much clearer, and to wear is comfortable. I was so sure about my decision, I bought 2 white CX 500's :-) The other one uses my girlfriend, she was amazed too about the performance. Some people wrote, it's difficult to open the package... It was cca 15 sec to cut the package around with a big scissor :-)
One more thing. When you order on the internet, buy from here (play.com). When you buy from somewhere else, check the package, and don't open, when it looks fake! It's easy to look after on the internet... (fake Sennheiser - search)
So I strongly offer the play.com and this product. I recommend, buy it now, and enjoy :-)