The action of the keyboard is excellent. Some may say it's plastic and stiff, but once you get used to it, it's a SOLID keybed.
I would say the significant downsides come from the features, with the arpeggiator and the chord function only being able to be used using NI software/Komplete Kontrol, which I found very disappointing. The pots for volume were fine, but I ended up just getting a nanoKontrol 2 since it comes with volume faders, a solo, mute, record, and pan knob for 8 channels. The pitch/modulation wheels feel like quality wheels, but that quality almost works against its utility. They feel good, but they don't move fast enough for a keyboard player like me (i.e vibrato using pitch wheel is very hard with this keyboard)
Personally, it's not within my workflow, and I would suggest even those looking to get a new midi keyboard or their first look for others such are Arturia or Novation. Way more bang for your buck.