Usually these kinds of puzzle games quickly become repetitive and become boring after only a few plays, but I think there is enough variation in Letter quest to keep me interested. The challenges give the player a reason to replay levels and the upgrades seem varied enough that I would want to keep playing in order to attain them. I had one issue with the level design because store purchases were used right after buying them rather than being able to select a turn. If I buy an upgrade I want to save it for when I can use it with a good word.
I have no problems with the interface and artwork. Seems like a good game.
I'm not a fan of early access purchases, but I put in my vote on Steam Greenlight and hope that Letter Quest is accepted.