I loved it! I found the switching to be super intuitive and the fact that score is based on travel distance kinda hints you away from spamming the OP biggest size. Good solution to a META strategy!
If I had to nit pick anything it would be that difficulty ramps up a tad bit too slowly, but it's no dealbreaker. Also, this is just personal and maybe not your cup of tea, but I would've loved to see varied weapons (like slow but wide shotguns, powerful but slow rifles, and such), instead of just a single machine gun with extra projectiles as upgrades
good stuff man!