I had time to use the Zen4s both in my studio and with personal monitoring live last night at a rehearsal.

First, I really dig the packaging and kit that you get. The Logo design, coloring, look and feel promote gear lust (legal by the way) and I was certainly captive to it. Very impressive. I really love the construction of the earpieces themselves—rock solid and easy to set in your ears.
Now for the sound. I listened to some recently mastered mixes of my own and it was jaw-dropping good... I’ve used some of the other contenders and I can say without flinching that none of them have the sound of the Zen 4.
I noticed, absolute high headroom with no distortion of any frequencies. The bottom was tighter than I’ve ever experienced without getting boomy and colored. The mids were astounding. Softer elements of my (and other mixes) were easy to hear, nothing was lost due to inefficient delivery. The highs were totally pristine without being harsh at all. I can’t say enough about the spatial sonics. It was a joy to listen to some favorite classics by the Beatles, Zep. Gabriel, etc. To sum up, the sound like a 100K stereo system on your head.