Just got an M32. I like that's it's portable, I love the DAW control, but I hate that certain things from the S Series MK1 are missing that I was not expecting (like the big browser window and the speed of scrolling).

The good stuff

• It feels great. Even though the keys are mini sized, they feel a lot nicer than a lot of similar sized controllers I've tried (such as the Akai LPK25). The buttons are clicky, and the whole unit is very light while still giving the impression of durability. I might have to get a slightly bigger bag to carry this around in, but it's much more portable than the 25-key controllers NI has made.
• The top half is exactly the same as an A Series keyboard. Same DAW integration (Ableton, Logic, GarageBand, Maschine). This means that using it with Ableton is a treat – I can control either session or arrangement view easily. And integration with Komplete Kontrol's app or VST plugin is great. Instruments can be loaded right from the hardware. And while scrolling through presets, you can hear real-time audio previews. This is definitely the coolest part.
• The small screen is very quick and responsive. On the S Series MK1, the LCD screens had a lot of delay between when your finger would hit a button and when the display would actually change to what it was supposed to display. This new mini OLED is much more responsive.
• The 8 endless encoders are touch sensitive, so you can touch one to see what it controls without actually turning it.

The bad stuff

• When browsing instruments/sounds, there is no pop-up window that shows off the thumbnails. On S Series MK1, which similarly did not have a color screen, pressing Browse would launch a large pop-up screen on your laptop allowing you to browse instruments with thumbnails and highlight which part of the browser was currently selected. The M32 does not do that, which is big disappointment for me. It's definitely been taking away from my workflow since I've gotten used to that feature.
• Because there is no pop-up window, this also means that you cannot sort your instruments by type (Synth or Sampled or Drums) or select an individual preset bank within an instrument. You can still filter your sounds down by specific instrument categories, but I like being able to visually see all my synth instruments in one place, all my reverb units in one place, etc.
• While scrolling through sounds, there is now a speed cap. On the S Series MK1, if I wanted to scroll all the way down to the bottom, all I had to do was spin the scroll wheel at top speed. Within a couple seconds you could make it to the bottom. Now it takes a lot longer, because at a certain speed, the rate at which you flick through presets will cease to accelerate.
• There is no light guide – not the end of the world for me, but I can see it being annoying for complex Kontakt instruments
• At 19" it's a bit long, and even though it's super light, it doesn't fit into my backpack. There are lots of bags that fit it, but you'll have to put a bit more work while choosing a bag to buy. Just something to keep in mind as I'm sure most of you will be buying this for the portability.