As always, there are a lot of theme suggestions, and relatively few that I like. That being said, the site and community generally do a pretty good job of paring down the ideas to a more palatable few.

Here are a few common things I downvote theme ideas for. If your theme is on this list as a "bad" example, sorry! That being said, this is all subjective, and different people enjoy different types of themes. I usually "yes" about 10% of the themes that come my way.

Main reasons I downvote your theme:

#1: Too specific

These theme ideas don't have a lot of room for interpretation, and generally force participants into one genre or narrative route. In my opinion, Small World fits in this category, and while there were a few different and innovative games for LD38, a significant portion were "little guy hopping on a little planet" rehashes. - apocalypse now - Candy will make you evolve - YOU are the princess waiting to be rescued in the castle - godlike llamas

#2: Too vague

Counter to my first point, some theme ideas are a bit too open-ended. A good theme idea acts as a sort of jumping-off point, and gives you a few game ideas in the first few minutes. - Most Valueable - Who are you?

#3: Enforces a particular mechanic or visual style

Everybody has their own favorite genre, visual style, or development environment. Putting limitations on how the game looks or plays not only discourages people who already have an established style, but also makes for a fairly repetitive playing/rating period. These can be great restrictions to place on yourself for the jam, but please don't force someone else to follow some specific visual or gameplay restriction. - 3D - Four Colors Only - First Person without WASD

#4: Make for a frustrating gameplay experience

Often, these also violate #3. They impose some restriction that often could be part of a really good game. However, it isn't something that I'd like to play 50 of during the weeks after the jam. Again, these could be good self-imposed restrictions on top of the LD theme. If I learned anything from Seven Pillars, it's that people generally don't like it when they can't figure out how the controls work. - Hard to control - 1 Button movement - Movement is unintuitive

Thoughts?

These tend to be the first things I think of to "disqualify" themes during Theme Slaughter, but occasionally things run counter to them. I actually rather liked Combine Two Incompatible Genres despite violating #3 a bit, and it resulted in some really good games.

What sort of metrics to you generally use, and how do you disagree with me?