Congrats on completing SHELL DEFENSE for the jam! Making and submitting your first game jam entry is a massive milestone, so you should be really proud of getting this across the finish line.
The art style is super charming and it actually looks like there was put passion into this game. I especially loved the weapon progression system—switching up the shell shots in the later waves added a nice layer of strategy to keep up with the tougher enemy types! The sound design with the ocean ambience and punchy shooting SFX set a really nice atmosphere, too.
I saw in the comments that you ran short on time for everything you wanted to implement, but honestly, as a foundation, this is solid. Expanding on this post-jam with a wave indicator/progress bar, maybe some upgrades, or a few more enemy movement patterns would take it to the next level.
Awesome job, keep creating, and good luck with the jam ratings! 馃馃悮