I don't remember playing Riddle School Series, and after looking at screenshots of these games they haven't impressed me much, but after this game I surely will play these RS Series. =)
Riddle Transfer is interesting game, has great animation and smooth work of its creator. It's also good, that it has more than one song, and songs are pretty good for this game, I think. Puzzles are also quite interesting and challenging.
I haven't liked only two things about this game:
1. I couldn't find this damned elevator key on my own, 'cause I was already used to labeled items and I just haven't checked this damned board with colored notes.
2. The story was okay, but haven't touched or interested me much. Also these conversations weren't so funny for me, if they even must be funny. =)
But overall I see that this game is great and give it 9/10.
And I love your special feature or how is it called. =) It's always interesting to read about the great work's creation process.