Forcing those classes to be singletons isn't really necessary. You just normally keep one instance of those classes around anyway. I actually think it's simpler to not bother with making them singletons. Plus there might be some instances where you want more than one instance of one of those classes. Like for dynaimcally loading one level while the player is in another.

class Application

Purpose:	Holds everything for the program
Contents:	Main program entry point function Game object Menus collection Form object RenderDevice object SoundDevice object

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

class SoundDevice

Purpose:	Same sort of thing as the RederDevice.

class ResourceManager

Purpose:	Stores, loads, and otherwise manages all resources.
Contains:	IResource collection

interface IResource

Purpose:	Abstract base class for all resources (such as graphics, sounds, etc.). Primarily used for keeping track of resources in the Resource Manager.

class GraphicResource : IResource

Purpose:	Contains a graphical resource.

class SoundResource : IResource

Purpose:	Contains a sound resource.

class MusicResource : IResource

Purpose:	Contains the stuff for a music resource. Not actually in memory as it would probably be a streaming thing. I am a little unclear on this one.

class Game

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

class Level

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

class Layer

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

class Tileset

Purpose:	Contains a full tileset.
Contents:	TilesetResource object Tile count

struct Tile

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

interface IGameObject

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

interface IUpdatableObject

Purpose:	An object that can be updated.
Contents:	Update function

interface IRenderableObject

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

class Player : IControllableObject

Purpose:	Everything related to the player in the game

interface IControllableObject

Purpose:	An object that can be controlled by user input?

class Menus

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

class Menu

Purpose:	The stuff for a single menu screen.
Contents:	MenuObject collection

class MenuObject

Purpose:	Some sort of base class for menu items such as buttons, edit boxes, etc.

There will be multiple tilesets used within a level?

Is IGameObject the same as I'm thinking for IUpdatableObject? IUpdatableObject can be used outside of the game though, such as for the menus.

I think we won't need a GameFrom class. A normal Windows.Form should be fine.

I know we need something for input, but that's not something I'm too familiar with.

Also I'm thinking the Game and Level objects should be both Updatables and Renderables.