Pretty enjoyable game! The story feels a bit weak but it helps setting the mood. Gameplay was fun, except for the holding down spacebar part :')
I think there may be a way to cheese the leaderboard if one is patient enough. The score is increased on kill, while the player level and wave level are increased when enough souls are collected. So, if one were patient enough, they could just sit on an easy wave and farm points but leave the souls alone, so there's not much threat from being overwhelmed by enemies. It would take a long time, but you'd get a top score eventually. I don't think it's a strategy you would want to reward players with.
Anyway, good job! :D I enjoyed it