Took a little bit of getting used to the gimmick, but once I got the hang of it, it was fun charging shots and getting close to large groups of enemies to clear out as many as I could in once charged shot. It probably also got me killed a lot because I kept getting too close the enemies, but we don't have to talk about that.
I do wish there were sound effects though. Also, I would definitely recommend adding some instructions or something in game, in the comments, or in a notepad document so that you don't have to trial and error keys to figure out the controls.