As game designers, we have a very natural, powerful, and rewarding tendency to design the shit out of things.
We usually have an equally powerful compulsion (as I'm sure most of your significant others will testify to) to share our creations with our audience and/or our families, that guy at the store, etc. Enthusiastic, passionate design is the fuel for our creative cars, and should be encouraged and embraced and protected.
HOWEVER. You know how you feel when you ask That Guy how the new Star Trek movie was, and pretty soon they are explaining to you the finer points of starship construction and interstellar treaties? And you were mainly just interested in whether or not it was a good Star Trek movie?
Guess what: your game, that you just made, and which actually got pretty good reviews...is That Guy. Your player just wanted to know if it was awesome when the good guy beat the bad guy, and your game sat there and listed off serial numbers and magazine capacities and planetary designations.
Not only is it annoying as all hell, but it is greedy. Your game is taking all my fun and hoarding it all like a fat, sloppy, cheeto-mouthed dragon. All the fun that you had while making this game, inventing this huge beautiful amazing universe...you just stole all that fun from me by predefining and forcing me to ingest every bit of that information before I'm allowed to finish the game. It is pedantic and greedy and embarrasing.
So, what's the solution? Just make a shallow game? Don't invent all the detail and atmosphere and history that is so much fun to invent? Eschew it all and just focus on gameplay? Obviously that sucks too.
Well, it's better than a lengthy, over-detailed manifesto, but it's still not great. No fun for the designer, and unfortunately, people have an intuitive sense for...depth, or something. They can usually tell if you've just created a shiny facade out of papier mache, dreams, and Red Bull.
I say go ahead and invent everything. Write up a binder, buy a new hard drive, create until your eyes bleed and your head pounds and your fingers cramp. But for our sake, for everyone's sake, keep that shit to yourself.
Only share the top 10% of what you wrote down or made up and stored away in your twisted brain. Share the top 5% even. Share the parts that might actually be better than what the player can invent on their own.
Give us just enough to set off our imaginations and join you in the fun of filling up your universe. Give us hints and winks and nods and nudges and keep your damn mouth shut.
Finally, if you want to check out some generous games, that slap greed and pretention in the face and don't apologize for it, these are my recommendations (these are all freeware examples):
stdbits by Mark Johns
God Came To The Cave by Cactus
Aether by Edmund McMillen & Tyler Glaiel
Knytt by Nifflas