Man, I freaking love games like this! As indie devs, we shouldn't restrict ourselves to what the mainstream considers a video game. Art games have been around for a long time and you really delivered a great one here. I really felt compelled to want to write a poem and the objects you create provide further inspiration for that poem. The world itself just stirs up your urge to create something. I love the concept of having letters as a resource and this also drives further creativity. Also, I really don't mind the UI and I think any shortcomings there just plays into the charm of the game. It's one of those games that is so far removed from what we typically see that it's hard to even come up with a critique.
Since you specifically asked for some tips on user interaction I'll give my two cents: The controls for rotating and scaling are confusing. You're forcing the player to have to break immersion and hunt for the right keys to transform it the way you want. A solution to this could be to keep WASD for rotation and use the scroll wheel for scaling. You'd have to set up different "modes" of interaction but that's pretty common and more intuitive. This wouldn't cover every transformation that you have but it's a start.
That being said, I think what you pulled off with those controls is perfectly acceptable. Fine tuning controls like that is a good bit of work and is not always going to come to fruition in a game jam setting. Especially with what you were trying to achieve.
Needless to say, I really appreciate this entry. Games like this are one of the reasons I love game jams! Great job!