I like the game a lot, its a great twist on boggle! (Have not played the other game it is based on) the campaign felt very easy compared to endless mode, which i did 2 times and my PB was 10.
I completed the campaign with over 400/500 health remaining, but I guess for players who are new to the concept the campaign needs to be fairly easy.
I do agree with the vowel thing, I think it should be weighted to give more vowels if you get unlucky with RNG because then you are just waiting for them to spawn in. (Or maybe just have a way to speed up the deteriation so instantly get a new hex on pressing spacebar to skip for example).
Congrats on getting the dragging so nice and the total level of polish is great too!