I think subcat is great idea. When I saw abandonia for a first time I didn't knew where to look for my favorite cat "tycoons and managemet" - strategy or simulation or unsorted... I'm for a minimal style of site though.

I have a few Edu games...

Edu is puzzle

But there are puzzle games (like Sokoban, Avish,...) and there are Educational games like (Daffy Duck P.I.). There are also some games in other categories that would be EDU, but aren't Puzzle - Stickybear Town builder, Playroom,...

Meh. I have Snoopy.

I think, there a only two possible ways to solve the categorizing problem.

a ) keep it simple.
Find five or six main categories and assign every game to one (and only one) of those.

+ good overview
o rough classification
- hard to find a field of similar games

Example: Commander Keen ==> Action
Websites: Abandonia (current)


b ) be as detailed as possible
Use a scrollbox with dozens of categories. Each game should have a complete(!) classification using multiple categories

+ find similar games based on genre, type, graphics, theme, setting, view, etc.
o more work with classification
- less easy browsing of categories (more like querying a database)

Example: Commander Keen ==> Action, Arcade, Jump&Run, Sidescrolling, Platform, 2D, 3rd-Person, Shareware
Websites: MobyGames (List of categories), HotU


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Personally, I prefer the second approach. That is, because you will never ever find the one perfect set of categories. Many games just won't fit into a single category.
What about System Shock?
- is it a 3d shooter? (1st-person shooting, lots of weapons and enemies)
- is it a RPG? (quests, stats and character development)
- is it an adventure? (storyline, inventory, cutscenes)

Also by using game genres as categories, you will miss other characteristics!
Ever tried to find games with ... say a Western theme on Abandonia?

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Whatever approach you decide for: be consequent!
Especially don't litter you current set with yet another category!


Edit: added link to MobyGames category definitions