the rhombuses can actually be shot from any angle, all that matters for the overhead mirror shots are that the target is infront of the platform, but from the first person perspective as long as you're aiming at a target on your platform it'll hit.
as for your game, i like the idea! I'll only talk about the controls and fun of it, since that's what you've asked for: I found it initially a bit iffy for control, and the sword feels a touch sluggish, but you get used to it, that's for sure. I think it's fun getting the cuts in, and I think you'll do well with this as you continue to develop it. I think if I had to give a suggestion, it might be something like mouse-based slashes around a radial, like if i swing my mouse to the left, i slash from right to left, swing from diagonally top right to bottom left, i swing that way in the game. That's what my brain wanted to do at least.
Either that or you'd need some level of introduction into the slashing for onboarding, so people understand how the slashing functions, but that'd be my suggestion.