The MK2 brings gives some of the more frequently used shortcuts their own dedicated buttons, and has a tidier panel layout since the LEDs are contained within the buttons themselves. It also has a different knob response - they allow you to scroll the full parameter range with a single twist, whereas previously you had to do many little scrolls or push the encoder down to traverse the full parameter range. The deadzone on the knobs is smaller, making it feel snappier again but also more fiddly to make micro adjustments and erase plocks. Headroom on the inputs is slightly improved, making it easier to set recording gain without losing sound quality. There are a couple of MK2-exclusive bugs: one where the current page indicator LED is too similar to adjacent LEDs making it really hard to read, and another where the input gain LEDs will flash by themselves when no signal is present. They keep promising to fix these but for now they still remain.
I had a love/hate relationship with my MK1, found it inspiring and frustrating in equal measures. Took a break and grabbed a MK2, had a much nicer time. I found the UI changes made a big difference even though I considered myself a ‘power user’, and the new knob response made it much more fun for fast performance edits. Felt like the whole thing opened up I found myself using it in new ways, playing it like an instrument more as opposed to just programming it. Still think the original looks better though, something timeless about that rugged black and red design. Good match for my Thinkpads!
tl;dr the MK1 will definitely get you there, but for me personally the more ‘luxury’ experience of the MK2 was worth the additional cash.