Funny how people think in similar ways!
I was thinking about creating a topic more or less like this the other day, but something got in the way.
Like with most categories and definitions there is no right or wrong. It simply depends on what you want to investigate.
I don't see any problems with RPGs falling into multiple categories. I think that is unavoidable.
A few thoughts on the current categories:
Horror: I like that Shesheyan included supernatural into this category. This allows for us to include games like Buffy, Angel,WitchCraft. Dresden Files etc which aren't strictly horror games. Alternatively we could have a separate category for these games.
Contemporary/Action/Spy: I sort of like how WotC included in their Modern line anything from 1600s to current day. Since historical is a separate category there is a question of where to draw the line. I would be fine with either anytthing after 1945 as modern or anything after the Cold War. The second option would leave things like James Bond 007 (published in the 1980s) as historical and I still feel like that belongs as modern.
Period/Historical: This one will often blend with Horror, Fantasy or Modern/Action/Spy, but I think it is still a useful category. I prefer somewhat broad categories so I dont think a strictly historical with no supernatural elements is of interest.
Cartoon (proposed): If we want to make this category a bit larger, I think comedy, parody and satire games could include most cartoon RPGs, although there are obviously cartoons that aren't humorous. Tales from the Floating Vagabond, Paranoia, TWERPS, Baron Munchhausen and others might fit in a comedy category.
One category I think is missing so far is the Cross-Genre RPGs. Not sure how popular these are anymore, but TORG and RIFTS are the main examples I can think of where the same campaign can include elements from multiple genres. Feng Shui might fit here too (YMMV). IMO that is significantly different from universal systems.
Maybe even a separate category for WEIRD rpgs like Over the Edge?
Anyway, I suppose there is no reason why you couldn't have BOTH broad categories and narrow categories that overlap, especially if we are talking about polls here on The Piazza. Let's go wild!