Having the player fight the boss in 10 second increments is a clever take on the limitation. The slashing through enemies bit is really satisfying, and for the most part easy to pull off. Though the fact that you move to where your mouse is rather than with e.g. arrows/WASD makes it a lot harder to aim without walking into enemies like a chump.
That's doubly problematic for the boss; with no way to stop shooting out the bullets (which is a cool way to encourage killing enemies, by the way!), I mostly just shoot them out into the void. And the boss moves towards me, which means I'm very often too close to move my cursor past him so the bullets hit, as he'll run into me. So that was a bit of a disconnect and a bit frustrating.