Here are my impressions.
I first played through the game on Alternative. I tried the first few levels of Normal after that, and was glad that I hadn't done it first.
The environments were appealing, particularly Old Ruins and Perpetuum Machine. I think that some of the backgrounds were too colorful, however, and broke the mood. Same with the stars in [whatever the area with the stars is called].
The game did not seem short. I was expecting it to be much shorter than it was, in fact, given the length of Nifflas' past games.
I would have liked to see more and harder puzzles. While the "action" challenges were quite enjoyable, to me the puzzles were much more so, but they were infrequent and very easy.
The story just got in the way, but it only did so at the beginning and end anyway.
I found six star secrets, and watched this video (http://www.youtube.com/watch?v=ssWwa4TiOow) but have not yet subjected myself to any other spoilers.