• The build quality of the NI MIDI controllers is significantly better than most
• The keybed feels significantly better than most
• The units have aftertouch

The Pitch and Mod ribbon controllers (if you're not used to them) may feel awkward at first.
Given some time... you can adjust and do things like simulated "hammer-ons", etc.

I was looking at getting either this or an AKAI Advance but I've decided to hold off. I was looking more at Advance because of the deeper plugin integration rather than being limited to Kontakt but part of the allure of Kontrol is the lights which I could run on key switches which would be very useful.
 
I'm now holding off because NAMM is coming and there are some rumours floating around already. I'm interested to see what is coming. Novation has been quiet the past few years and I'm hoping for a huge reveal that puts both AKAI and NI's controllers to shame. ;)

The only criticism I have is the fact that it's not USB-powered. Guess it has something to do with the lights. But that's the only flaw for me.