Very good
Wasn't able to crack 3-2 and 3-4. The fact that I played lvls 3-x is very telling.
The sound effect for connecting isn't the best. And it was very devious of you to make the "Continue" button on the lvl finished screen not lead to the next lvl, a bit silly of you I would say.
Oh, and connectors are a bit unintuitive, after experimenting I was under the impression that you need to drop both parts for them to connect
Otherwise, extremely good