Summary

Honestly, I had no clue what was going on, it was way too confusing and I basically rage quit after three tries.

What I liked:

• Because of the confusion and rage quit, I sadly couldn't find anything I particularly liked

What I didn't like:

• No tutorial
• No music
• No sound fx
• The controls were on one page, but it was a confusing layout. 
• No clue what the UI was telling me
• Art was too simplistic

So-So:

• I couldn't find the theme connection due to not being able to play it the way you had intended it to be played, but looking at the screenshots and "merge" (although I couldn't merge at any time, I tried), seems to suggest that there's some connection going on.

Closing:

IMHO, a proper tutorial would have served you the best here. No music/sound fx, that's ok (not fine, but if the rest was great, it may be overlooked slightly), not everyone can get that in or source it, and not everyone's a great artist, but when the gameplay is so frustrating that no one has a clue how to play it, that's where a lot of issues start to unravel.