I loved the sound effects and the idea, I did have a few issues though.
(One thing though, I for some reason started with 2 million energy per click? Not sure if this is intentional since in the screenshots it looked like you were getting 20 per click)
Sometimes when several planets spawned at once and went in the same direction, I found that the planets I had already destroyed were blocking the planets underneath and I wasn't able to destroy them, so maybe having them instantly destroy rather than slowly fade out would be a bit nicer.
Another thing is, the planet's don't really seem to give that much money which doesn't make stopping clicking on the portal to click on a planet worth it. Not sure if that's what the "Upgrade Planet" button is for since I didn't notice anything different when upgrading it.
That's really it though, I loved the visuals and sound effects. Sorry for the lengthy comment, but great game overall!