This is a great start! I made few adjustments and (hopefully) clarifications. I'm assuming we use some kind of Singleton class, but I haven't yet figured out a clean way to do this with C#.

class Application : Singleton

Purpose:	Holds everything for the program
Contents:	Main program entry point Game object Menus collection Form object Render Device

class Game : Singleton

Purpose:	For everything in the actual game (as in part of the gameplay), and nothing else.
Contents:	Level object Player collection

class Level : Singleton

Purpose:	For everything in a single level.
Contents:	Tileset collection Layer collection Object collection

class Player : IControllableObject

Purpose:	Everything related to the player in the game

class Layer

Purpose:	Contains the arrangement of tiles that make up the level.
Contents	Tile collection

class Tile

Purpose:	Represents a single tile on a single layer
Contents:	Tileset index Tile index

class Tileset

Purpose:	Contains a full tileset.
Contents:	Tile collection

interface IGameObject

Purpose:	Abstract base class for all dynamic objects in the game.

interface IRenderableObject

Purpose:	An object that can be rendered
Contents:	Reference to a Graphic Resource through the Resource Manager

class ResourceManager : Singleton

Purpose:	Stores, loads, and otherwise manages all resources.

interface IResource

Purpose:	Abstract base class for all resources (such as graphics, sounds, etc.).

class GraphicResource : IResource

Purpose:	Contains a graphical resource

class Menus

Purpose:	For a system of menus.
Contents:	Menu collection

class Menu

Purpose:	The stuff for a single menu screen.

class GameForm : Windows.Form

Purpose:	Just the standard empty form there to be used for drawing. Doesn't really contain anything. May be able to just use System.Form directly.

class RenderDevice

Purpose:	Interfaces with the graphics library for all the rendering.
Contents:	All stuff needed for the graphics library Reference to the form to draw to