I have only really played one game, Minetest Tutorial, but I think it should be included by default, because it is the most logical way to get started in the Minetest world. Also, it is beautifully designed and really useful as a teaching tool to learn the basics of the game.
I also vote for "Tutorial" (both game and map) to be added in the game. (i didnt want to write that much, so i quoted) (there shouldnt be too many unneeded subgames, else minetest will take a way too long to download)
Do not call me -minetest. Call me DS or DS-minetest. I am German, so you don't have to pm me English if you are also German. The background is a lie.