I think the objective could maybe be stated in the game itself. To add to that, I seen a bunch of useful information about the game on your itch page as a reply to another person.
I could just say general statements like 'make it more fun to kill enemies', 'make the robot arms more interesting', but I think the main thing you should work on is giving the player a sense of purpose. Why am I killing these enemies? How does that impact the player? What do robot arms do? What are these orcas? It seems you have a general storyline or idea about all of that, but it isn't conveyed in a meaningful way, rather than adding length to the arms.
To add a few positives, the arm idea is pretty cool, and congrats on finishing a game! You did what most game developers fail to do, you actually finished a project! I can see the game being pretty fun to revisit, later in your game dev journey, after you make a few more small games, and learn from those experiences. Keep at it! :)