@odjn
I'm guessing the reason the person who made this wont put mouse support in because its Retro. Which kind of means "old" in case you don't understand. Because back in the old days PC games didn't support the mouse for games like they do today I think thats also the reason why its WASD en arrows instead of WASD and mouse.
BTW: even if the game looks like Geometry wars. Who cares? I could also say that WoW is a Rip-off of Diablo 2 but it doesn't matter because its different in its own way. Just like this game is to Geometry Wars.