Text sizes need some work, e.g. the upgrade prices.
The economy could use some balance, unless there's some strategy I'm missing.
It's quite fun to make a bunch of different words. I got up to a lexicon of 562. But making random words seems to be at odds with making the target word. It can be pretty slow and unrewarding to make the target word, as it's just a temporary boost that often doesn't compensate for the suboptimal configuration you have to make, but also filling out the lexicon seems to offer no reward.
I don't find research to be a worthwhile thing to do because once you're past a certain point, cycling the tiles to other letters doesn't cost very much.