I would make some joke about girls and squids but I won't, I'm glad to see Splatoon being so succesful and I think most of you have explained very well why is so appealing.

With that said

:)

http://dynasty-scans.com/doujins/splatoon :)

It sounds simple but the best way to appeal to a new audience is to not intimidate them. This is why the Wii performed so well. You keep down information overload, you make the objectives easy to process, and you keep new users from being frustrated and feeling like fools.

When the message is, "go out and spray paint everywhere," you've basically accomplished all of that. A deeper understanding of tactics can then come naturally as the person plays the game.

I think that's Splatoon's primary key to success, especially in a market where a lot of your fanbase doesn't really know the shooter genre all that well. It's really a very clever way to attract players who might be scared off by an IP that appears to be more complex. It's really all about presentation. Even the lack of voice chat is going to keep people from feeling intimated and embarrassed by players who are more skilled.

Although, I tried to pinpoint all of my reasons specifically for Japan, while that is very much something that can be said for all regions, imo.