At least now people won't bitch that Nintendo doesn't invest in new IP's. They have all along!
2012-Nintendo Land-fail (though high sales on Wii U credited as bad launch title)
2013-The Wonderful 101-fail
2014-Tomodachi Life- N/A
2015-Xenoblade Chronicles X and Splatoon

It's friggin' brilliant. The world doesn't need another Mario game, and Nintendo desperately needs to show that it create new experiences with new characters...

I'd be happy either way.

Mario Paintball would have been nice, using existing characters as they have in every other Mario spinoff franchise, though the ink-travelling/swimming mechanic wouldn't have made much sense. The squid-people look fine and give off a Jet Set Radio vibe, so no complaints from me there.

Personally I don't understand the continual call for new IP's, Splatoon would be the same (i.e. a new shooter game with a fresh twist) regardless of whether it was a Mario spinoff or had completely new characters. It's the gameplay that makes an IP fresh, not your avatar.