Most of the internet agrees that Apple's bundled headphones are terrible, and you should get then replaced ASAP. Lots of sites recommend these for those on a budget, so I felt it had to be done. And I'll tell you what, they're brilliant.
I am fast becoming an audiophile, but I don't have the budget to be blowing £1000s on headphones. But these are excellent considering they are under £30. Bass, mids and trebles are all there in equal measure, with none of them sounding too overpowering or harsh. I'd actually put these ahead of my Bose in ear headphones in terms of quality sound.

Now, what about durability? In the past, this is where Sennheiser have let me down. I had a noise cancelling pair of earbuds similar to the CX300s, and while they were pretty good for the money, the left earbud stopped working after a few months. But so far, I've had no issues with the CX300s whatsoever. However, the cable does feel a little thin, but it does seem to be withstanding all the abuse I've given it so far.

One more thing, the cable is asymmetric; one side is longer than the other. It is a tad annoying but not so much that it detracts from the overall experience.

In short, get a set of these to free yourself from the dreadful bundled Apple earbuds and start to listen to your music, rather than just hear it.