Not showing what your current in-progress string does is definitely weird - I mostly just Enter'ed after each letter and rewrote the whole string again and again. Would be arduous for whomever has a slower typing speed, so seeing it immediately change (like Pheonix suggested) would be great. In fact, Enter doesn't really serve any purpose in this demo, it could just auto-enter after each change in the string.
Overall, I liked the demo but felt like it was even slightly too drawn out so I doubt more puzzles would do it any good - but more letters is cool and I really liked the finale! Final runes used: 84.