Overall, the game has promise. From what I was able to play, I had fun. I agree with what Oles said, so I'll just add onto it.
The main problem I ran into is the game seems to crash randomly after attacking an enemy. It was never consistent, but the new enemy introduced 4 or 5 levels in would always crash the game. Needless to say, I wasn't able to finish the demo because of it.
Overall, I though the mechanics worked well, but I did find it kind of odd that you had to go into a specific square (their back) to attack instead of just occupying the square they're on. It's not a deal breaker, but It does feel a little arbitrary and a bit of a lazy way to enforce certain setups. The spirit can't hurt the lantern, so why go behind for a sneak attack?
Visually, the game looks great, props for the art! But, I did have some issues with game-play related feedback. I think the main reason is the relatively small game area on-top of an already small resolution, making the spirit enemies hard to differentiate, and making their silhouettes harder to make out at a glance. I'd get sniped thinking I was out of range of the sword, but it turned out it was I was looking at an archer.
All in all, I look forward to seeing the game once it's polished up and expanded. Nice work so far!