Well, I have now gone through a little less than half of all the themes, and it's not looking good...

My current kept : slaughtered themes is currently 1:88. And after seeing thousands of themes, I now have a set of filters which I check every theme against to see if I should spare it or slaughter it.
Filter 1: Does the theme make sense? / Is it not totally dumb?
This filter basically weeds out all the themes created to troll the slaughterers(does that count as a word?). It eliminates things like "FlOaTiNg IsLaNdS", "nuzloke"(whatever that is), and "Mushrooms and ducks do it again". This one is pretty simple and obvious.
Filter 2: Does the theme add unnecessary constraints?
This filter can be broken up into 3 smaller filters:
A. Does the theme constrain game genres?
One of the intresting things when playing other submissions is seeing how the same theme is interpreted diffrently. I don't want to play 20 platformers or 20 puzzle games. One good rule of thumb I heard is this: "Can you think of a platformer, a puzzle game, an FPS and a text adventure that fit this theme?".
Example of a bad theme: If you jump you die
B. Does the theme constrain the "Style" of a game?
Some "Styles" of games are: Sci-fi, Midieval, etc. A theme like "Weird Sci-fi" limits the possible styles, and reduces overall game diversity.
C. Does the theme constrain the Dimension of a game?
Realistically, there are 2 types of games*; 2D and 3D. Which game you make is mostly a matter of personal preference. Therefore, the theme shouldn't force LD participants to use one or the other.
Filter 3: Is the theme too vague to be a meaningful inspiration?
The official purpose of the theme is to help people overcome the "Blank Page" challenge. Themes that are too vague undermine this purpose, which is why "You start with nothing" fall flat.
After these filters, the themes you keep or kill is a matter of preference and judgement. A good example of this are the many COVID-19 themes. Most people don't like these themes and automatically downvote them.
I hope this guide will help you think of better themes and help you in your slaughtering :D
- There are 1d games like zrox