Good luck learning GameMaker! I recommend you looking up «GameMaker Studio 2: Complete Platformer Tutorial» playlist by Sara Spalding on YouTube. That was my starting point. Many things from these videos are applicable to top-down games as well.

As for your game, I recommend the following:

1. Collisions. There're lots of invisible walls, which are irritating. Remove them)

2. Hitbox. It's hard to aim when you're not moving.

• Make the player object turn to the direction you're moving. "image_angle =  direction" for step event must help.
  • Alternatively you can make it face the mouse cursor — "image_angle = point_direction(x,y,mouse_x,mouse_y)".
• Make your attack hitbox match with player's direction. So the player can always tell, where is he going to hit.
• Change the player sprite, so it's easier to see the direction.

3. Camera. Don't pin the player to the center of the screen. Tutorial mentioned above must help.

4. Bounds. Don't let the player go out of view either (you disappear if you go up or left in the starting room).

5. "Landmarks". It's hard to tell if you're moving or not, when you're passing through long corridors. Since nothing is moving on the players screen. The easiest fix would be adding some background objects there just for visuals.

Btw idk what game engine youre using, but theres probably an easy fix for the blurry pixel art, so id recommend looking something up for that. also youre able to skip enemies, i was able to win in sub20 seconds doing that lol

I got confused and assumed the red circles were blood cells. It would be nice to distinguish the enemies in some way. I would also randomly get stuck in the middle of the path and would need to move up or down a little to continue.