Sorry for the late reply, I had to go on a business trip last week...
Totally. :3 Well, once again, I'm still interested in what you meant by mood if you feel you could elaborate a bit more on it.
Thanks for insisting, because this forces me to think about what I meant myself and to make a stronger statement than just talking about a cloudy word like "mood". First, however, please allow me to digress a little bit.
Some time ago, I set myself the challenge to make a game character consisting of only 4x6 pixels and a single color. It took me quite a while but eventually I came up with this running animation which at the time I was quite pleased with. It consists of only three frames so it isn't totally smooth, but you could argue it's another achievement in terms of minimalism.
Now, there are many good reasons I can think of to pursue such an endeavor. BUT! Ultimately we have to ask ourselves: what's the point of all this? Because while it's fun to challenge oneself and to work within self-imposed restrictions (be it palette, resolution, you name it), these are probably nice "finger exercises" but what does this actually add in terms of making a good game?
Because that should be our goal: making a good game.
Exercises are good, just like a painter practicing sketches and making studies before taking on a monumental painting.
So it's not about setting oneself arbitrary goals: Hey, let's see if I can make a 1-bit color depth game! Well, of course you can. It has been done before. You can
always make some kind of game no matter what the restrictions are -- but the hard part is making an
interesting game that people would want to play. And the point I'm trying to make here that reducing complexity through constraining your ways of expression doesn't automatically lead to a good game.
Take a look at "Pioneers" here in the forums. The author, Eigen, decided to restrict himself to use only 4 colors for the whole game. Well, but that alone doesn't mean anything. It's how he's pulling it off, given that color constraint, that makes this game really cool. Otherwise, people would just look at the game and go: "Oh, wow, he's only using 4 colors? Cool!" And two minutes later they'd move on to the next game... unless the game is fun to play. You don't get any brownie points for doing it in 4 colors -- you still have to create an interesting vibe, an engaging atmosphere, like Eigen did.
Now, in addition to what I said above about artificial restrictions making good finger exercises but not necessarily being good instruments to base an actual game on -- that should be taken with a grain of salt: I don't believe there is only "one way" to make a game, it really all depends. As a matter of fact, especially in game jams where the time to make a full game from scratch is limited, people often enjoy to develop the game organically, as they go. They start with a certain premise and then run with it. To me, this style is reminiscent of musicians improving together. Maybe you start with a melody or a rhythm or something else, and then you see where it can take you. Why should that not also work for video games?
But at the same time it's clear that this approach lends itself to certain types of games better than to others. In any event though, I think it's more difficult to keep a consistent, convincing gaming experience if you develop the game in the improvised, more reactive style. Unless it's a very small game. Now back to the actual topic...
You say that you want to evoke emotion in the players of your game. I think that's a very good approach. But then maybe the first question to ask is "what kind of emotion?" Because I believe the mood of a game is a big factor of steering the emotional experience of the player.
Let's take for instance a look at two very successful mainstream series, Uncharted and Tomb Raider. All titles in these series are at a basic level very similar games: running around, some platforming, some shooting action, mild puzzle solving, story driven. But they transport very different moods! For instance, compare say Uncharted 1 to the latest Tomb Raider reboot - both games share aspects such as having you run through ruins and jungle-like forests. But right from the opening sequences of both titles, the mood is very, very different: you have the sunset, hawaii-shirt style of Uncharted 1 that feels almost like a TV detective show from the 80's. And then you have the mysterious, very dark atmosphere of Tomb Raider's ship wreck back story. Similar game mechanics, completely different moods!
Of course, a game's mood is more than just its graphical style. Sound effects, music, level design, etc. all contribute. It's what makes making a good game difficult but that's also what makes it fun. This is where game making is not just a technical, but an artistic endeavor.
In the end, to me, "mood" is what remains in your head even years after you last played a game. You won't think back to "Tomb Raider" and go "yeah, that was a fascinating story-line" or "oh, that one puzzle was so clever". You will more likely think of the island, the sea, stormy weather, the emotional stress the character you play goes through... and then in a second thought, maybe, about specific scenes you remember. If that is true, then maybe it's a good idea to ask yourself: "what is the association I want people to remember about my game?"
At the same time, I think stuff like this can also very easily lure you away from ever shipping a product if you wax philosophical from day 1 to a point where it inhibts progression. So my advice would be to take this middle path and think about the mood of your game and how to create it as one important aspect of development without obsessing over it.
The End.
Sorry for going crazy in this post :-)