Serious

Not to be mistaken with serious games, which is a videogame genre of sorts instead of literary tone.

Related:
* Faux serious - similar but ultimately more comedic
* Bleak - this is more for the visual outlook
* Survival horror
* ... most other real horror games (as in, not things like Addams Family)
* ... most war games

Contrast:
* Humorous
* Lighthearted

Generally speaking games that try to be serious, largely devoid of humorous jabs or comic relief. These may seem oppressing or depressing for some. Humor may exist, but infrequently and/or hidden or otherwise not immediately apparent or so misplaced it may not seem funny to most people (except maybe out of context).

Easter eggs, or jokes that easily go amiss or just are out of place (they're hard to laugh at) should not be a reason to not add this tag. Cheerful, colourful, cartoonish, etc. appearance may also be included in this tag as long as they fit the general idea of being serious.

Does NOT mean the games aren't fun to play, only that they take or try to take the subject more seriously than others. The so called serious game genre is similar, but they are prone to eliminate the fun to play bit, nor are these propaganda/advergames like them. And unlike the serious game genre, these may be somewhat unintentionally as serious as they are, or it wasn't the main goal but more of a side product to accomplish other goals.

This does not mean that you specifically can take everything in the game seriously, that tends to be failure in immersion, either on your or the game's part. Also, some people fail to take anything seriously, so their opinion on the matter is not very significant.