Pros: dynamic, deep bass, relatively balanced, analytical, good soundstage, very inexpensive
Cons: slightly recessed lower mids
I won´t repeat what everyone else wrote before - because it´s true. I´ve listened to a Beyerdynamic DT990 once and while I love my Sennheiser HD-600 a different cup of tea would be nice sometimes. But then, Beyerdynamic headphones are a bit too expensive for the sole reason of being able to listen to "another flavour". Thank God there is Superlux. You´ll get so much material for your money. You´ll also get very good, Beyerdynamic-like sound. You can even improve the sound if you replace the pleather earpads with the velour pads for the AKG K-240. I don´t know why but they sound a bit more balanced and refined with these earpads. Further improvement can be achieved by putting paper tissue between earpad and cup (increases the distance from ear to driver and will likewise improve comfort).
If you do these two things you´ll get a headphone that will rival headphones for 150-200 Euros: they are dynamic, precise, crisp, balanced with a very good soundstage. They are easy to drive but they will sound best with good amplifiers. They won´t be impressed by loud or harsh music, they will just play along with just the right amount of directness. Some people would argue that this makes them sound a bit "bored" - which sounds almost insulting to me because they are anything but boring. People seem to confuse balanced sound with boredom. Well, let me put it this way: if you want your headphone to colour the music you´re listening to... go and search elsewhere. The Superlux does indeed add a bit colour (around 7.000 Hz) but it´s not very much and it´s not distracting. However, lower mids seem to be a bit underrepresented - but I could be fooled about that because I´m accustomed to the comparatively (to the Superlux) warm mids of my HD-600.
All in all, very, very good for the money. A true bargain, thank you Superlux.
P.S.: before I forget... they need considerable burn-in time to sound their best.