The best parts of the game will have to be the overall presentation and vibes:
1) Love the audio and the simple visuals you got going. The sound design is particularly a great standout, with the gushing blood. Its SO SATISFYING when you kill a lot of enemies in one grenade and the blood just spills EVERYWHERE.
2) Vampires seem to be a common theme around with the draining health, very straightforward implementation of the theme - nonetheless very understandable and serviceable.
3) Improvements I imagine would be implement more audio cues, such as when the grenade is ready, instead of having to look to the top left everytime so we as palyers can be more intune. Some sort of indicator the next shoot is ready as well. Generally giving more player feedback mechanism would be nice!
Otherwise, enjoyable, and occasionally hilarious with how much blood is going around.