Definitely one of the better shooters out there!
The upgrades are a big part of the fun and are effective to the gameplay. All the effects and sounds, the smoothness of the feel and mechanics, are all beautiful and work very well together. I would definitely be interested in some lore implications, maybe a reason as to why there are spirits you have to defeat?
Truly a great job overall! It reminds me of another great shooting game with upgrade-based gameplay, Pixel Wars: https://mrrobotthemechanicalman.itch.io/pixel-wars