Hey, I really liked it!
On the first two levels, the "Win in X turns" value is marked as 0, so it's hard to know exactly how many turns, except by exceeding the number of turns. The difficulty is quite high as most of the enemies deal really high damages, but after a few tries, I managed to finish all levels (also, it's the kind of game I never play, so don't take it into account, haha). Also, a better way to understand range (attack range, movement range) would be appreciated, as I took a long time on the first level to understand where I could go (maybe a step count (Wakfu/For the King/ etc.)).
Being able to skip the cinematic during Chapter 3 would be nice because I failed multiple time on this level and having to watch it again and again is a bit lenghty! Also, and I know it's just a demo, but I couldn't understand why I need to complete the optional objectives, I don't have any bonus or malus completing them, so I just decided not to do them, a reward could be appreciated! Concerning bugs, nothing special, just the NPC's body glitching through the map once dead, but nothing too important.
Except for all that, I really liked the prototype, and it would be worth pursuing into a full-length game with more diversity in characters, weapon types, adventure, (magic ?), etc.
Good luck with all that!