Summary: Excellent noise-cancelling headphones considering they can be found for a good deal if you search hard enough. While sound quality and performance sans-battery isn't up to Sennheiser PXC 450 level, most people will find these are a worthy and decent performing purchase
Pros: Sound quality; detachable cable; good build quality; effective noise-cancelling.
Cons: Horrible sound quality when batteries die; can become uncomfortable after extended wear; sound can leak badly at higher volumes.
Conclusion: A solid entry into the noise cancelling headphones space, Panasonic's RP-HC500s offer good value for money, although those willing to pay a premium should look towards high end IEMs for better sound quality.
Pros: Smooth overall sound, good noise cancelling
Cons: Clarity issues, a little too strong in the mid range