Here are some simple yet engaging 2D game ideas that can provide a unique and enjoyable experience:

### 1. **Time Traveler's Quest**
**Concept**: Players control a character who travels through different historical periods. Each period has unique challenges and puzzles.
**Gameplay**:
- Solve puzzles to fix anomalies in different eras.
- Collect artifacts and upgrade your time machine.
- Engage with characters from various time periods who provide clues.

### 2. **Mystery Manor**
**Concept**: A top-down mystery adventure game set in a haunted mansion.
**Gameplay**:
- Explore rooms, collect clues, and solve puzzles to uncover the mansion's secrets.
- Avoid or confront ghosts and other supernatural entities.
- Use various tools and items to interact with the environment and progress through the story.

### 3. **Eco-Warrior**
**Concept**: A game where players take on the role of an eco-warrior tasked with saving the environment.
**Gameplay**:
- Travel to different locations and complete tasks like cleaning up trash, planting trees, and saving animals.
- Use tools and power-ups to tackle environmental challenges.
- Educate players on environmental issues through engaging gameplay.

### 4. **Shadow Ninja**
**Concept**: A stealth-based platformer where players control a ninja navigating through a series of levels.
**Gameplay**:
- Use stealth to avoid enemies, solve puzzles, and reach the level's end.
- Employ various ninja skills like wall climbing, shuriken throwing, and disappearing in shadows.
- Collect items and power-ups to enhance abilities.

### 5. **Sky Islands Adventure**
**Concept**: An open-world exploration game set on floating islands in the sky.
**Gameplay**:
- Travel between islands using various means like gliders or airships.
- Discover hidden treasures, solve environmental puzzles, and complete quests.
- Interact with island inhabitants and trade items to progress.

### 6. **Pixel Chef**
**Concept**: A cooking simulation game with pixel art graphics.
**Gameplay**:
- Run your own restaurant, cook dishes, and serve customers.
- Manage time and resources to keep customers happy and earn money.
- Unlock new recipes, ingredients, and kitchen equipment as you progress.

### 7. **Dungeon Alchemist**
**Concept**: A rogue-like dungeon crawler with a twist of potion crafting.
**Gameplay**:
- Explore randomly generated dungeons, fight monsters, and find ingredients.
- Craft potions to gain various abilities or aid in combat.
- Combine different ingredients to discover new potions and effects.

### 8. **Starship Mechanic**
**Concept**: A space exploration and ship repair game.
**Gameplay**:
- Travel between planets and space stations, repairing and upgrading starships.
- Solve mechanical puzzles and mini-games to fix various ship components.
- Manage resources and navigate through space hazards.

### 9. **Lost Civilization**
**Concept**: An archaeology-based puzzle and exploration game.
**Gameplay**:
- Explore ancient ruins, decipher hieroglyphics, and uncover artifacts.
- Solve environmental puzzles to progress through different archaeological sites.
- Learn about ancient cultures and history through engaging gameplay.

### 10. **Cosmic Rescue**
**Concept**: A space-themed puzzle platformer where players rescue stranded astronauts.
**Gameplay**:
- Navigate through space stations and asteroids, solving puzzles to reach stranded astronauts.
- Use various tools and gadgets to overcome obstacles and hazards.
- Manage oxygen levels and time to successfully complete missions.

Each of these ideas can be expanded with unique mechanics, storylines, and artistic styles to make them engaging and enjoyable for players.