I like the visual style and flair, the colours add a lot to the atmosphere. As does the music, sounds like some ghost party for real.
Is it intended you can hold down space and wake up all the ghosts as you pass their graves? Feels like it's not because then you could just forget about this mechanic all together. Also it think you have enough time to scan the entire graveyard, no matter how many graves there are, so there's no challenge involved. To fix this, how about you need to spend some time at each grave to actually wake the ghost? That would give some significance to the number of graves in a level.
Speaking of the time limit: I am confused by "before dawn" (in the description). When in the game, the background sky becomes brighter and darker a few times before the time is actually up, so as fas as I'm missing something there's no clear indication of how long until the party's over.
It's also hard to track which graves where visited and which not. A little indicator to make them distinguishable would help a lot!