really interesting little concept, bullet hell + tower defense is something that could be a great little mobile game!
I also really liked the implementation of the theme. Definitely one of the best I've seen there.
The art is clear - no issues with visibility at all.
There's a menu!! And a tutorial! And an exit button! You're already above about 50% of steam games ;)
I actually don't think I can really complain about anything. This is rare for me, I've usually got some constructive criticism... An incredibly minor gripe, but I don't think the isometric angle works too well for this sort of thing, top down would be better - but that's a VERY minor thing. It works well enough, I just got a little confused by depth and position xD