The MX 660s from Sennheiser are the descendants of a long line of headphones that have proved enormously popular.  This latest version includes several new features, some of which are more welcome than others.

No More Solid Case
The MX660s are fairly comfortable to wear, like most traditional headphones.  Once you've added the foam pads, each headphone stays firmly in place in your ear and shouldn't fall out if you move suddenly.  In black and silver, the MX 660s are discreet, which is something of a blessing, as, close-up, they look a little cheap.

The least welcome change on Sennheiser's part is the decision to swap the hard plastic case for an imitation leather that looks like a small purse.  Your headphones will almost certainly do better inside the pouch than thrown into the bottom of a backpack or shoved in a pocket, but for high-end headphones, you could do a lot better.

Loud and Clear
The MX series has always been known for excellent sound quality, and these MX 660s don't disappoint.  The treble is very clear, as is the mid-range, but neither dominates.  It's true that the bass is a little weaker than it could be, but overall the audio experience is impressive, and easily trumps a lot of entry-level in-ear headphones.

The MX 660s aren't bad headphones; in fact, they're very good.  But when you know just what Sennheiser is capable of, it's reasonable to expect a little more.