Simple base for a platformer game. Some points of feedback I would say are adding variable jump height so how high you go depends on how long you hold up for. Also making the player stick to the floor when moving on slanted platforms would probably be a good idea here since you move horizontally faster than you fall making you unable to jump if you happen to press left or right slightly before jumping. (it's a setting in the characterbody node) Also if it's not implemented coyote time and buffer jumping helps platformers feel a lot better to play.