I really like Counter-Strike and its level editor, Hammer. Thanks to the Unity engine, I believe I've achieved a combination of both: the easiest way to build 3D game levels and play quickly.
In this game, you can create a garden in sandbox building mode and then place some robots to play with you. After switching to FPS mode, you can compete with the robots in the garden and buildings.

Game Features:
1. Use the easiest way to build a game level scene.
2. Play FPS games in your own scene.
Note: After editing the scene, keep a support point under the camera before testing, as your starting point is the current position of the camera.