Pros: Comfort, bass
Cons: Poor mids, sometimes too much bass, crackle
I should disclose that I purchased these headphones for $15, and for that price I recommend that anyone snatch them up as a back up, or workout phones. However, not sure that I would purchase them for $60 or even $40. These headphones really struggle with mids, and sometimes the bass is flat-out overpowering. I like to test out my headphones by listening to Pinback, as their music is a good representation of the aural spectrum. I found that the bass (which under normal circumstances should be almost an afterthought in a Pinback song; I have heard the drums in their songs described as "percussive breathing") took over the rest of the song.
Isolation on the CX300s is a mixed bag. I use these on my train commute and find them more than adequate to block out the train noise and other passengers; however, the cable noise is sometimes too much to bear.
Anyone looking for a quick and dirty upgrade over stock headphones should consider these, especially at the price I paid. If you are looking to spend 40 or more I would keep looking.