My three kids, ages 12, 7, and 2 all enjoy this app. My eldest plays with it just because it's fun, my middle is still learning some aspects of the content, and of course my youngest is just gaining exposure. The story "book" sent by email after we registered was brilliant! My youngest really got excited to play the game after we read the story, and having names for the numbers was really handy. We have wished that there were more stories about them.
I've actually just finished playing the whole thing also. I found it to be a lot of fun, much better than hanging out on my usual social media. I found the way that the stars would finish some puzzles to be annoying after a while, though my 7yo is quite tickled by that feature. I actually started to avoid the starred areas, though that ended up meaning that I often didn't build any of the larger numbers, because usually larger numbers were starred rather than smaller ones. But I had a lovely time playing with this app, and my kids will likely keep playing for a while to come.