Great work on this new look! I must say that I liked the Space design as well, and did not think it was childish, but am very pleased with the new look too. Here is what I like:
The new colors. Nice shade of yellow and nice shade of grey.
The shape of the icons during the learning sessions, especially the audio session buttons.
The new look of the flowers.
The sleek and simple- but not overly simple- design is pretty, but does not distract from the material that I am learning.
The new app icon looks pretty cool.
Overall very pleased with the new look, new colors and the new style. Keep up the good work!