Pros: Fantastic bass quality and quantity, Mids, Detailed and smooth treble, Airy with no closed-in feel
Cons: Clamping force is a bit high (but this is a portable mini-headphone, so if they don't clamp enough they will fall), sometimes uncomfortable
This is one my favourite headphones. They have fantastic build quality, are inexpensive, require little voltage to be driven properly, are small and discreet, and sounds better than some pricier headphones (IMHO).
They also are completely non-fatiguing, and great all-rounders. They don't make bright and thin recordings sound even worse, but instead make them much more listenable. A complete win from Sennheiser. Bravo.