Important: Here the mid production Sextett (MP) is described. This is recognizable by white passive membranes, but with orange plastic behind and a orange colored driver. The early production (EP) has everything in orange, the last production (LP) everything in gray/white. I assume for the review that you have already taken a closer look to the headphones. The test configuration can be found in my signature.
The AKG K240 is rough, aggressive and forwarding, while always exciting. Localization sticks close to the head, everything on an axis between right, left and center - nothing is far away. The AKG points out things that even more expensive headphones (linear tuned Audeze LCD-2C as comparison) present only subtly and quietly, while the K240 leaves out finer details. But the AKG is smart: The music is not reproduced correctly because the frequency response is treble dominated, while it sounds like there is more detail, but in combination with the very "direct" sound characteristic, the most basic details are simply louder.
The strengths are the reverberation, the resonance of instruments and the transient reproduction - this makes it so incredibly realistic to listen to. In every recording you can hear how big the recording room was, whether there was a lot of echo in the room or not. All hiss, hum and crackle are unforgiving represented. In live recordings you can hear the audience bumping glasses or moving chairs. The audience is suddenly louder, where this was still in the background with other headphones. To reproduce this at such a high level requires far more money. The AKG dissect the music, there is no other way to write it.
It's not the best headphones I've ever heard, also I would say that it is beaten pretty fast in the 300€ price range in terms of details and pure spatiality. But the AKG is able to make me put down the high-end headphones and get into listening with the AKG, simply because it's so special.