My impression at PAX East earlier this year was that it was...too easy? But such a joy to watch, so maybe it won't matter. It was hard to tell where I was at in the arc of the game, but by "too easy" I mean I started to feel disconnected from the gameplay because it was asking so little of me.
I got to play their demo at Gamescom, and I feel similarly about it.
I didn't really get into the gameplay, but I'll give it the benefit of doubt - at Gamescom they left the indie game stations mostly unattended, so you could play as long as you wanted and as much as the game allowed. I played the first 4 levels, and felt some sort of progression, while not really a challenge yet. I could see the game building up more challenge in later levels, it would be great to read reviews clarifying how many levels there are.
I stopped at level 4, because I am a polite person, and a nice Korean gentleman was queueing behind me.
Hope the game delivers, it's a looker for sure.