GAMEPLAY: I died somewhere around Wave 6, and while I was impressed by the smoothness and responsiveness, I was starting to get bored of the formula. Maybe the upgrades could do more shaking up, maybe the enemy types could be more diverse, or maybe I'm just not good at the game. Regardless, what you have is well polished.
VISUALS: I love the filtering and camera swivel, as well as the overall neon look that ties in well with the game's theming. With a game this fast-paced, it was hard to tell where walls were or what each enemy's type was. I'd at least like to see the pink trim be the exact boundaries of the level, instead of there being a black boundary. Enemy sprites could be more strongly colored as well, or have a stronger glow behind them.
AUDIO: With the theme of the game, you needed good audio to sell it, and I'll say you've certainly passed the mark. I died too quickly to really see how my health affected the music, so I can't comment there.
THEME: Using XP and health as resources isn't the cleverest implementation I've seen, but it certainly fits the bill. Maybe this could be taken further with other types of upgrades, like mentioned in GAMEPLAY.