Pros: Sounds great, comfortable, plenty of volume with my HTC Rezound
Cons: Factory cable not optimum for portable music players
I bought my HD-518 after Christmas to use with my HTC Rezound Android phone at work. I spent hours researching headphones and finally concluded that the HD-518s were a good bet to meet my requirements for good sound, good comfort, good build quality, and reasonable cost.
The only thing I didn't like about the HD-518 was the 6.3mm (1/4") plug and long cable. Fortunately, Sennheiser is now selling a shorter replacement cable with a 3.5mm plug.
I have to say that the HD-518 and short cable work well together and sound great to my ears. I've spent lots of hours listening to a wide variety of music at work (mostly on Spotify), but some from ripped WMAs from my own CD collection. The HD-518s have met my expectations so far.
For those who might be interested in the replacement cable, the Sennheiser item number is 5X8SHORTCABLE. See this head-fi article for more info on the cable.