Got mine yesterday and couldn't do a lot of impressions because my ears were still ringing from seeing Q-Tip Sunday night. Rocking them today though.
I'm not going to comment a lot on the sound because a bunch of people already have. I will say that they're amazing. Best IEMs I've heard, hands down, and that includes the UM2, Image X10, SE530, and super.fi 5 pro. The bass is definitely there, which makes me really really happy.
The sensitivity is definitely less than the UM2, which is a good thing. I still hear some hiss when plugged into my MacBook Pro, and I've been playing them on the lowest volume notch, but it's reduced enough that I won't have to cringe every time I listen straight from my laptop like I did with the UM2 (which exhibited loud hiss, blown-out sound, and excessive volume on even the lowest volume setting).
About the ergonomics, the cable is definitely a little slicker and more flexible than my UM2. I don't know if that's because it's new or because they've actually changed the cables, but it's a definite improvement. The cable is also a bit longer from joint to earphones as well as a couple inches longer from joint to jack. Also and improvement, in my opinion.
The earphones themselves, which I always thought looked bigger than the UM2 in pictures, are not in fact bigger. Their design is more rounded and tapered, making them slightly more comfortable.
The biggest change between the UM2 and the 3 is definitely the length of the stalk which the tips sit on. The stalk on the 3 is significantly shorter, such that to get the same seal, I have to angle the 3 more inwards to my ear canal than I did with the UM2. I was afraid the difference would necessitate a change in tips, but fortunately I can still use my medium Shure soft-flexes (which I have a nice little stock of). If anything, this change may turn out to be positive. I think it makes the earphones less likely to become unseated when I wear a winter hat, and (possibly) reduces the tendency for pressure and positioning to cut out the sound when I sleep on my side with them in.
In short, I'm in heaven and don't envision buying any new IEMs until at least the Westone 4
. My UM2 will be up on the for sale forum as soon as I get around to it.