The glittering effects and the upgrades likened to constellations were great fun to play.
It's good that you inevitably create constellations as you repeat upgrades!
The explosions felt bizarrely strong!
That, and the fact that enemies were quick to spring up at relatively close range and objects were scattered around the edges of the screen, making it difficult to move around.
Also, the FPS dropped drastically once combined with the trail, probably due to the heavy burden of the explosion effects!