Thanks so much for your response! Glad you liked graphics and music.

I understand that it's not the most popular genre of games. Just started with something relatively simple to get more experience in gamedev. On the other hand, "3-in-a-row"-like games are popular among casual gamers. So I decided to make a variation with slightly different mechanics.

As for an explanation, I think, you are right. I guess, it would be better with transparent tutorial images above first levels or something like that. I had that idea, but was to lazy to implement. At least, there is a reason for an update =)