I recently bought the Beyerdynamic Custom Studio headphones, and I must say they're REALLY GOOD. This was me moving up from the Sennheiser Momentum, which are great, but still only entry level for audiophile headphones. I absolutely love the soundstage, richness in detail, and clarity with these new cans. The bass is defined - and of course, adjustable - but I really do love how the vocals stand out. Try playing The Beatles' Hey Jude off a CD or flac with an appropriate amp, and it's heavenly!
I was actually comparing these at dedicated headphone store in Toronto with various others, including Grado RS1e, Grado SR225e, HiFiMAN HE-400i, Sennheiser Momentum....
The Grado SR225e was the most clear and vibrant out of all of these, but lacked the sound stage I was looking for, and bass was a little too weak on them as well. I also couldn't afford headphones that were $700 PLUS tax.
Ultimately it became a showdown between the HE-400i and the Custom Studio, and after about 45 minutes of comparison and song testing, I found the Custom Studio to be my choice based on overall sound quality and wearing comfort. The HE-400i had a tad better soundstage, but the CS still had better, more vibrant sound without being coloured, and details stood out to me more. Bob Marley's guitar riffs had texture I couldn't get from the HE-400i. The sound of the HE-400i sounded somewhat dull in comparison - a little too mellow for my tastes. Custom Studio sounded powerful, balance, yet totally natural. Wow.
All in all, I love my Custom Studio cans; the output they produce is beautiful without impacting my wallet so brutally. I was still able to afford a DAC amp for my PC and a portable amp as well. In my (limited) experience, Beyerdynamic create gold within the $300 range for headphones.