lol what? no...

^ I like this answear. 

Adventure/puzzle with spooky theme, ment to be kid friendly.
This is not a horror game.

Not really it's more a puzzle/adventure game, I wouldn't say you feel dread and such when playing it.

It's more funny than scary, so no.
As others have said, it's a puzzle/adventure game with some spooky elements thrown in. It makes for a great game for the kids and adults to enjoy during leading up to Halloween.

Is as much as horror than something like the Goosebumps movie. Is more an adventure with kid-friendly horror elements added.

Nah... Luigi's Mansion isnt even Goosebumps level of horror.

You know, unlike most people here I had the pleasure of playing this game as a kid and it could get tense sometimes.
Ghosts jumping out of nowhere and of course the famous blackout.

I could see it as a horror comedy maybe? But only the first one, which has a thicker opressive atmosphere at times. Dark Moon is more in line with something like Hotel Transilvania, where it's horror-themed but not meant to be "scary" in any way.

No. It has a spooky theme (in a cartoonish way), but certainly not something I would classify as horror. Though I found the final boss in the first game to be kind of creepy when I was younger.

Probably ghostbusters-level scary.

Yeah that stopped my playing of the game right there when I was a kid. Oh, not because I was scared, just couldn't figure out what to do lel.

@OP: Maybe the first game could be scary for children, but definitely not Dark Moon and most likely 3 as well. Kind of a shame but I prefer Halloween spooky over horror spooky, if that makes sense.