It's very rare to find an independently made game that both has good pixel art AND competent programming, and this game definitely has both.
The level and enemy design, although there aren't much of either with the shortness of the game, are great.
The character animations and usage of slowing down or briefly pausing the game for certain actions makes attacks and hits feel like they have so much more impact. The game feels good to play!
It's a bit of a bummer that there is only one boss, but I know first-hand how much time it can take to make a game, and for something made in 5 days, this is more than good enough as it is.