No doubt we'll need a visual editor at some point, but having this kind of API for the "engine" makes rapid prototyping a breeze.

gistfile1.cs

scene.Children.Add(new GameObjectBuilder()
	.WithMeshSource(b => b.Mesh(new Mesh(Content, "Cube")))
	.WithMeshRenderer()
	.WithBoxCollider(b => b.Size(new Vector3(10, 10, 10)))
	.WithRigidBody()
	.Position(new Vector3(100, 50, 100))
	.Rotation(Vector3.Right, MathHelper.Pi / 8.0f)
	.ToGameObject());