Upfront caveat: I have tinnitus and I'm not a highly sophisticated listener... so... with that in mind...
I just got these two days ago. I LOVE them. Absolutely the best headphones I've ever owned.
My retail box was very tightly packaged, and it took a few minutes to get the lid off (seriously). Sturdy and well-packed are adjectives that come to mind. The shipping box is definitely made to protect the headphones well. Good job Sennheiser!
The USB charging cable is pretty sturdy. You can charge the headphones one of three ways: 1) plug it into your computer or laptop; 2) use an automobile charger adapter; or 3) use a wall outlet AC adapter. It would have been really nice if Sennheiser had included both adapters, but I guess you can't have everything. I had a spare AC adapter lying around, so I used it.
No matter how excited you are, let the beauty charge up for 3 hours first. You'll save yourself some frustration, trust me. While it's charging up, download the full instruction manual from the Sennheiser website and read up.
The headphones' 3.5 mm audio cable felt a bit on the thin and flimsy side. However, as long as you exercise normal caution and care with it, you should have no problems.
There is only ONE LED on the cups. At first I thought there was another LED that wasn't lighting up by the power switch, but no, there is only ONE LED that lights up either red, purple or blue (depending on the charge state and the pairing state). It might be a good idea (like I did) to use a small flashlight to see everything clearly, or just use a strong overhead light.
The volume switch doubles as the check-battery-status switch and the phone calls switch. This leads me to a small nitpick.
Sennheiser gives you pictographs to show you exactly how the switches work. They, of course, give you a legend to show you how to interpret the pictographs. By the way, don't bother with the Quick Start Guide. It uses the pictographs all over the place, and it will only confuse you until you download the PDF file (full instruction manual) from the Sennheiser website. You do not get a full instruction manual with the headphones, so, again, no matter how excited you are, just download it from the website and your life will be easier.
Also, make sure to download the Sennheiser Updater to update the firmware. That's at the main website also. On edit: As of Nov. 7th 2015, there is NO firmware update or Sennheiser Updater software update, so for right now, you can skip this step.
Despite my minor nitpicks, the build quality is truly outstanding. With reasonable care and caution, they should last you years.
Needless to say, the audio quality is superlative. These are the best headphones I've ever owned. They are very comfortable on my ears, which are average size (I guess) for a tall man (6 feet 3 inches). My head is, I guess, average sized for my frame.
