AKG Acoustics K240 Monitoring Headphones

I'll start off with the cons:

1. They are large (not suitable for smaller heads)
2. Hard to drive (600Ohm will do that)
3. May be uncomfortable for long periods of time due to relatively thin pads
4. Non-detachable cable
5. May sound shrill to some because of bass roll-off and bright treble

 
That's the cons. That's all of the cons.
I've heard headphones above and below these in price, but none have matched the open, precise soundstage, clear definition of sound and sheer amount of detail in these beat up old cans. The cable died a couple of times, the pads had cracked due to age and were replaced. When I replaced them, I tried to find something as close as possible to the originals, to preserve the sound signature. They are still uncomfortable for long usage and I still don't care.
If I would ever consider writing a love letter to a pair of headphones, these are the ones. I probably wouldn't have the heart to tell them they have any cons, and certainly wouldn't start with it.

When I compare these to the newer Studio K240s, these win by a long shot. Not only in neutrality and detail, but in build design too. 
The Studios have a big mid bass hump that makes everything sound boomy. But the Monitor version has a very balanced frequency response that sounds almost perfect. To me, the treble is very good, but I dislike the spike most AKGs have in the 8-9 kHz range, these included. Although not as apparent with classical music (which these are great for btw), rock and pop and singing definitely is sibilant after a while. That being said, the treble adds to the detail retrieval, which may be why these are meant for studio monitoring use. I also LOVE the mids on these, and they are the phones strong point. Mids are better than the HD 600s IMO. That being said, the soundstage is kind of small compared to many headphones, but still ok. 
I also have noticed the bass could be a little more, as it rolls off quite a bit in the sub bass.
 
EDIT: 6/3/14
I have tested these with both the ODAC+O2 combo and my vintage Nakamichi TA-2A + CDP-2A. Sounds amazing with both of course, but I prefer the Nakamichi as it powers it better and gives a little extra bass boost and it also smooths out the treble a bit. It's also meant to be driven from those kind of sources. With the ODAC+O2, its a little sibilant and bass could be a little more, but this is because of the neutrality the O2 brings. This headphone would do quite well with warm dacs and amps. 

Background:
I was looking for a studio monitor headphone for under a hundred bucks, I was going to buy the AKG K240 Studio at first but saw these "Monitors" on eBay for much cheaper, for 59 bucks I didn't hesitate to buy them although I was nervous about the 600 ohms impedance. They arrived in perfect condition with the elastics still having lots resistance, and the ear pads without any cracks, however the golden labels at the sides had fallen off (common issue). I hooked them up to my HK 3490 receiver which were being fed Apple lossless files from my computer through my uDac 2. After three minutes I was ready to return them, everything was muffled, mids, treble, bass, absolutely terrible. I was curious, and took off the earpads and the filter, what I saw shocked me. Literally half an inch of this strange dusty, black residue gunk was everywhere, it covered the six circles around the driver and was also on top of the actual driver, I think this was the dried up residue of the adhesive they used 20 something years ago to attach the cloth to the plastic. After giving both sides a thorough cleaning and dusting out the filters, they had transformed into something else. 
 
Bass- It's there, reaches quite low but isn't too emphasized and can be muddy at times, but not terrible at all. I listen to lots of bass driven music (rap, electronic) though I wouldn't call myself a basshead and I'm quite satisfied with the bass these put out.  
 
Mids- What these headphones excel at, a bit forward but never fatiguing, very clear and detailed, upper mids could be better. 
 
Treble: The reason why these headphones are never fatiguing is because of the rolled of treble. The lack of sparkle in the treble gives female voices a sometimes "dark" sound, I myself don't like a treble assault on my ears with headphones so I don't really mind this as it lets me listen to them for a long time but for you that want that pronounced treble, nothing a bit of EQ can't fix. 
 
Soundstage: Excellent, I can distinguish locations of instruments in live performances, and also where people are firing at me from when playing Call of Duty 
 
Comfort- I love the self adjusting headbands on this, not a lot of clamp, however these won't come off your easily, I have a slightly large head and these fit me well, I often forget I'm wearing these. I just wish the earpads were deeper and had more cushioning, my ears sometimes press against the drivers. 
 
Build Quality: Excellent, headband is solid, plastic used is sturdy, gold accents give it a sense of quality, leather is also soft on the ear pads, besides if these weren't well built how could they have lasted 20 something years?
 
Aesthetics: One of the greatest looking headphones ever made. 
 
Design- Are you kidding me? The K240 series is one of the most famous and successful headphone series' of all time spanning five generations: Sextett, Monitor, DF, Studio and MKII. 
 
Bang for the buck- $60 bucks for this type of sound quality is unheard of, even if you pay 90 bucks these are still a great deal.
 
Overall: A solid choice for a used, cheap monitor. After 30+ years, the K240 is still a studio standard.
 
 
Bass- 4/5     Mids- 4.5/5      Treble-3.7/5       Soundstage- 4.5/5      Comfort- 5/5       Build Quality-5/5        Aesthetics- 5/5        Design-5/5      Bang for the buck- 5/5    Overall- 4.5/5