Better than cheapo headphones or PC speakers. But they won't beat (or equal for that matter) a decent set of set of stereo headphones (at music) for the price. To make use of all the speakers either use upmixing software, or some older Medusas have a switch to change from 5.1 to stereo mode (marked DVD/CD). Either technique improves the music quality a little. Generally the sound is well-defined and you will hear all the details on a recording but they lack a certain something ('warmth' I guess).
I would highly recommend them for films and games but calibration using your soundcard software is important (especially setting the bass crossover frequency, as shown on Speedlink's site).
I find my Medusas to be very comfortable. I've had them about 2 1/2 years and used them regularly. Even now they sound as good as when I bought them, with little significant sign of wear and tear.
As mentioned by myself, and others, in previous threads, something thing that may spoil your music listening is the interference picked up by the amp (from WiFi, mobile phones etc). It's really difficult to eradicate entirely but can be reduced significantly.