Pros: Great sounding, comfortable, reasonable price
Cons: Plastic frame, thin cord
I just got these phones delivered a couple of days ago and have enjoyed burning them in and listening in intervals all weekend. They seem to benefit quite a bit from burn in, as most headphones do. What length of burn in time optimizes them? I don't know, but hey have improved all weekend. They didn't sound bad right out of the box, but the extension, clarity and sound stage across the spectrum have all gotten better with each hour of burn in and listening time. They are very accurate, open and transparent sounding to me.
Some reviews I've read about the 598's have bemoaned the lack of bass response, but I find it to be just about right for my taste...tight and extended, without the overemphasis of some phones I've heard. I listen to a broad range of music from blues to rock, alternative, metal, jazz, fusion, funk...and even a bit of country. They perform well across the genres I listen to.
The only cons I listed (Plastic frame, thin cord) actually also add value. The cord could be a little thicker I suppose, but it is very soft and pliable, and detachable and user replaceable if damaged. The plastic frame makes these extremely light and comfortable to wear for extended listening sessions. The color scheme is a bit over the top for my taste, and I wish they came in basic black too, but as I'm not looking at myself in the mirror at all times...especially when listen to music...this is a very minor detail.
I also own a pair of Denon D2000's which sound good to me as well. Compared to the Sennheiser 598, they are heavier, hotter to wear (due to the thick pleather earpads), and are more bass emphasized. They are both good entries in the mid-priced headphone market, with the Sennheiser's edging them out the Denon's for the money in my mind. I haven't decided which I really like better.
I listen to vinyl, CD's, Apple Lossless, and iTunes Plus (256 kbs AAC). In my mind, musicality and listening enjoyment decrease slightly with each format as listed, which only becomes apparent when you do a side-by-side listening test. 256 kbs files sound very good to me, although there are certainly deficiencies that become apparent when listening with better headphones, speakers and amps. Over time and evolution, this has prompted me to re-rip my CD's into Lossless format, and only buy CD's and rip them to Lossless moving forward (rather than buy downloads from iTunes). However, even the iTunes downloads sound better...as good as they can, given their limitation...with the 598's over lesser phones or earbuds.
I have only had these headphones for a few days but already I would recommend them to anyone wanting a solid performer without breaking your bank account. I look forward to many hours of enjoyment from these phones.