I really enjoyed this game, but I can't figure out exactly what I liked about it? It felt like it was the exact right length to showcase the mechanics, even if those mechanics aren't all too complex. This game just feels good to execute - moving around and shooting enemies. The sound effects add to it well; and the music choice fits perfectly. The sprites are cute as hell.
One small thing is that while the camera tilt and the 2d-in-3d environment is really stylish (especially the sprite flips), I noticed that the controls were slightly inaccurate because of the camera tilt. It wasn't anything too bad, but this is definitely something to think about.
The tag-team-to-swap mechanic isn't wholly original, but it's been implemented in a very satisfying way in this game. Good work!