I'm new to game design and have been reading many of the recommended links here, trying to get a sense of what all I will need to do to eventually create a game. One issue I've continually come across is the 2d vs. 3d one. I don't necessarily need high-end graphics for the game I want to create, so I'm trying to understand each a little bit better.

I understand that old Nintendo games were 2d. I also understand that top-of-the-line modern games like Call of Duty, Halo, and Skyrim are 3d. But what are some of the most complex 2d games and some of the simplest 3d games?

How about old PC games like Tropico (the original)? Railroad Tycoon 2? Sim City 4? Are they 2d or 3d?

My main goal here is to figure out what the maximum potential are with 2d graphics. It's obvious in the extremes, but I'm curious to see if I can create what I want with a 2d engine.

That being said, more and more projects who use 2D art, are starting to use 3D modelling software and some scripts to translate the 3D art to 2D sprite sheets.

Personally, my decision maker for 2D vs. 3D is: "What type of game is it? and how will that affect the art / look"

I don't have a whole lot of time, and would rather spend it programming than in a 3D modeler such as blender or 3DS Max.

Also, my art skills suck, so I try to stick with 2D as the assets are so much simpler (for me) to make, and animations are fairly simple.

The best way for me to do a simple game is 3D models with 2D mechanics, for example: A 3D pacman, 3D bomberman, 3D pong, 3D tetris, etc

Simplest 3D graphics:

The physics are 2D (despite the heightmap), even square objects like the house are circles in the physics engine:) The game eats half of my CPU. If it would be written in the proper way it should only use 10-20%. Despite of this this its a great game.

(I dont think you meant as simple as Wolf3D, or Doom1)

More simple 3D:

Complex 2D:

If you are just "trying to get a sense" then you shouldn start with an engine, ....or with a 3D game. Almost every 3D has simpler 2D versions. (Minecraft -> Terraria)

I am making my first "big" game in 3D (with my own engine). Now, I am finishing it.

One problem which I encountered are assets, much more assets per game object.

In 2D game you have animated sprites. In 3D you have models, textures and animations.

The engine is much more complicated, as well. These things costs time and/or money.

So, it is easier to make a good appealing 2D game.

Thanks for all the advice and info to everyone that responded. It's been very helpful.