"Let's say we want to make a 2D game with no shaders, no nothing. Like a pacman or snake"
Then use Flash , it's the best option for that type of game.

For a 3d game with no shaders and older type graphics or technology , then use GameStudio or Unity(though they do support shaders as well, but they're easier to use and less demanding of end user PCs).

If you want to make the next block buster game with top of line graphics and want to use the best and most powerful engine you can get your hands on , then use UDK.

UDK is powered by Unreal 3 Engine , UE3 was use to make Unreal Tournament 3, Gears of War , Mortal Kombat vs DC Universe , Tom Clancy games , ect...
It's a powerful engine that used to cost three quarter of a million dollars to license , now at our hands. But if your looking to make corny pac man clones , then stick to something like flash , cause even GameStudio is way too powerful for that.