Please study the examples one by one, sorting is intentional.
Basic (nographics)
Create a simple world with three objects and one component each.
Learn: GameObjects & Components
2D Quad
A single rendered sprite in 2D.
Learn: SpriteRenderer, Sprite, Slicing.
2D Quad (sliced)
A full sized sprite, and a sliced sprite.
Learn: SpriteRenderer, Sprite, Slicing.
2D Quad (advanced)
Two rotating sprites, with non-square aspect ratios.
Learn: SpriteRenderer, Sprite, Transform.
2D GUI
Intermediate mode GUI via OnGUI().
Learn: OnGUI.
Physics Simple (nographics)
Simple physics example with a ball falling & bouncing on the ground (no graphics).
Learn: Rigidbody2D, Collider2D.
2D Physics Simple
Simple physics example with a ball falling & bouncing on the ground (2D).
Learn: Rigidbody2D, Collider2D.
2D Physics Simple with Interpolation
Simple physics example with two balls falling to the ground, showcasing interpolation.
Learn: Rigidbody2D, Collider2D, Interpolation.
2D Collider Gizmos
Physics example showing runtime Gizmos around the colliders.
Learn: Collider2D, Gizmos.
Keyboard
Simple example to show the input system: press any button.
Learn: Input, OnGUI.
2D Pong
The first simple, 2D Pong. WASD to control the left paddle, arrow keys to control the right paddle.
Learn: Physics, Input, OnGUI, Gamestate.
2D Arkanoid
Arkanoid clone in 2D. Use the left & right arrow keys to control the paddle.
Learn: Sprites, Physics, Input, Gamestate.
2D Minesweeper
Minesweeper clone in 2D: left click to uncover, right click to flag a field.
Learn: Sprites, Input, ScreenToWorld, Gamestate, Global Components.
2D Snake
Snake clone in 2D. Use the arrow keys to control the snake, eat food to grow.
Learn: Sprites, Input, Spawn/Despawn, Prefabs, Physics Collisions & Triggers.
2D Whack-a-Mole
Hit the moles as they appear, as fast as you can.
Learn: Sprites, Animations, OnMouseClick, Colliders.
2D Bird
Flying bird, use the Space key to flap the wings.
Learn: kinematic Rigidbodies, Gravity, OnCollision.
2D Ants
Ant Simulation in 2D, with food & pheromones.
Learn: global components, simulations.
2D Tiled Basic
Import a map from Tiled map editor, including animations.
Learn: TileMap, Tile.
2D Tiled Advanced
Import a map from Tiled map editor, with advanced features like multiple tilesets, layer opacity, etc.
Learn: Tiled advanced features.
2D RPG
Lightweight RPG example with Player movement, Monsters, combat, health, a Tilemap with colliders.
Learn: Tiled, Animations, State Machines, NavMesh, Interactions.