The combo counter is also your health, so if you mess up your combo, you'll die in one hit. Normally I would say that punishing players that are struggling and making life easier for skilled players is kind of backwards, but enemies also get faster the higher the combo is, and slow down when the combo is dropped. Interesting ideas!
You also don't take damage right away when touching an enemy, instead you get a zoom in effect before you take the hit. I think this is a bit overpowered, because if you keep running at full speed, you'll be able to pass right through enemies and their attacks without getting hit. Then again, if there are a lot of enemies on screen, their attacks can overlap, and then this trick doesn't work as well.
Deflecting bullets with a sword is fun, and there's a thing where a bullet you fire will sometimes fire more bullets of it's own and wipe out everything nearby, but I don't know how to trigger it. You can also double jump, and 'jump' by swinging the sword up. Alternating between sword and gun attacks is also faster than just using one or the other, and I like that.
I'm describing mechanics like this because the game doesn't tell you anything, leaving you to discover all the little nuances for yourself. I actually like that, but not everyone will.
I was going to give a lower rating, since the game doesn't have a huge amount of content and because of that thing with the delayed contact damage, but I think I just talked myself into giving a higher rating. Not bad!