It's strange, but when I think about it, DK1 was a much more positive 'product-y' experience for me than DK2 was. Perhaps part of that is that DK1 was my first VR headset, so much of the initial awe factor had worn off by the time I got the DK2.
The DK2 was/is plagued with software teething issues. Totally acceptable as it's a developer kit, but still frustrating and a little worrying. The other thing I found disappointing coming from DK1 to DK2 was the vastly decreased field-of-view. I think it's a combination of things that contribute/contributed to that (over-zealous vignetting in the earlier SDKs being one of them), some of which may have been fixed since in software. I say this as, to me, the Gear VR FOV seems wider than DK2's despite having a slightly lower quoted value.
My DK2 is basically a brick now. There's been a compatibility issue with AMD cards running it in extended mode, which goes all the way back to September of last year which has not been fixed on my system by any driver updates or Oculus SDK updates since. Given that the cool stuff I'd like to use with it (specifically VR Desktop and VorpX) doesn't support direct mode and only does extended, I've almost given up on it (this affects dev too - I believe the latest Unity editor still doesn't support running stuff in Direct-to-Rift mode from the editor, for example).
That's an acknowledged AMD bug which is fixed but I don't believe it's available yet. Oculus v0.6 apps can always just run in direct mode and avoid that problem.
