These definitely aren't cartoon phones, meaning that everything is an over the top and exaggerated for effect. I'm finding that the more I get accustomed to listening to these headphones, the harder it is for me to go back to a super up-front presentation because the music starts to get agitating. The Zune earbuds I listen to now start sounding loud and gaudy. I can listen to one or two songs, jam for a little while and then I turn the music off because some of the shrill elements really start to get annoying.
What's most amazing is that these phones are just as listenable when you are going to sleep as when you are awake. In fact, they even take on a special sort of magic when you lay back, close your eyes and allow the music to wash over you. The smooth sound these Sennheisers deliver are especially a pleasure for the ears when you are in a relaxed environment.
A more balanced sound takes some getting used to after being accustomed to after listening to unbalanced music where some element completely dominates over the rest. The main singer isn't completely overshadowing the rest of the songs, and a strong instrument like the electric guitar isn't so prominent that it's all you can focus on. These are pushed back to give the other sounds more emphasis. It seems a lot of people share the impression that after first hearing the HD600, they think, "What's the big deal? I hear all these rave reviews, but I don't see what's so spectacular?" But for some reason, they never take the headphones off and keep listening... and keep listening... finding more and more they start liking. And finally, after a long while, they look back and say, "Ahhhh so THAT'S what they were talking about!"
I just wrote this for soon-to-be HD600ers in order to prepare them for what to expect. You hear the rave reviews and your mind gives you expectations to be blown away with aural pornography... However, you're likely to find these phones a good bit more gentle if you're coming from some of the other brands. Once you sit down and start doing more and more listening, that's when the nuanced, balanced appeal of the HD600 phones really come through. The benefit isn't all up-front. It's spread across a longer time span. It's amazing how well these phones get even better the higher the quality of the equipment you put behind them! I'll be building around these phones for a long time.