I had heard that this was a tough game well before trying it, and those rumors were indeed true!
But I feel like that's been mentioned to death, so I'll just skip over that part for now.
Graphically, the game looks really nice. The character portraits are great, and the character and enemy sprite are all good. The environments don't stand out, but look good and stay out of the way of the action.
The audio may be from an asset pack, but it's used very well. The music is hype and helps make the battles exciting!
The gameplay is really fun, I enjoyed the melee, ranged, dodging and time-slowing powers. It could get a little confusing and frenetic at times, but always felt good. (Edit: If I had one time critique about the combat feel, the hits didn't always feel like they had a ton of "impact". Maybe stronger SFX, more graphical feedback, or some screen shake could notch it up! This is mostly a nitpick though, forgot to mention it when I first typed this.)
Well, felt good until the difficultly finally did me in. I could make it to the diamond shield room, but the waves in there trashed me every time. I do want to give it another go later though, as it was very enjoyable overall! I know you're planning to added checkpoints, so I'll absolutely give it another spin then, if not sooner.