The concept for the gameplay was really interesting and I want to see it explored more. The movement with the dashing was a bit awkward and confusing to control, but I understand the idea and was able to work with it for a little while once I played with it a bit.
Aesthetically, the game has potential; the changes between the nether world and its enemy-projectiles and the "real world" with its spiders were a cool way to introduce variation into the style. I would like to see a lot more changes introduced from wave to wave, however.
The audio was good; the sound effects were perfectly fitting, though sometimes they started and cut off at awkward times that didn't quite make sense. I still liked them though.
The implementation of the "Lightshow" theme was decent because the light your orb attack introduces to the screen and the light of the netherworld enemy-projectiles all stand out pretty vividly, although the fact that these elements are "lights" doesn't impact the gameplay much. I'm not sure if you tried to incorporate the "Only One" limitation, but the fact that you have "Only One" weapon did feel pretty significant because it was so easy to lose it when you use it and have to track it down again, as well as having to "recharge" it (in a sense) in the nether world, in which you can't use the thing at all. The precarity of that felt important.
Good ideas all around.