I'll use Innovation defined by innovating, or: make changes in something established, especially by introducing new methods, ideas, or products. I also warn ahead of time that I am a fan of Nintendo, so I may very well be biased.
I feel you can consider to aspects of a game when thinking about innovation: The core gameplay and the framework. I am going to use CoD as an example of the standard because it is currently the best-selling shooter franchise of all time. The bog standard of a shooting game is one that has realistic guns, with a main drive to shoot directly at something. Therefore, the main innovation would be from weapon variety or from the shooting mechanics themselves. Splatoon I feel emphasizes this the most because not only does it use a unique weaponry in the form of waterguns, giant paint rollers, and paint-tornado bazookas, but it also changes the shooting mechanic itself by making it based on a fluid that people can track as opposed to bullets or explosive projectiles.
The second part I feel every game in the poll does to a certain extent, I just personally prefer Splatoon's. Territorial control has been done in shooters before, but never quite as literal as painting your territory, and I don't think there are any other shooters ever made before where you can turn into a squid and swim in your own projectile. Also squid map jumping to an ally's location or recharging your ammo faster by being inside your ammo are just refreshing gameplay mechanics that also add to Splatoon being innovative and unique.
To those who want to learn more about Splatoon, Nintendo themselves have uploaded three lengthy gameplay videos of it from the Treehouse event:
https://www.youtube.com/watch?v=SxcLLFbmJHE (General Gameplay)
https://www.youtube.com/watch?v=_4JL5H7XMKY (Developer Q&A)
https://www.youtube.com/watch?v=kycn7GBqoFs (Developers vs Treehouse Members 3-Game Match)
Current Consoles: Gaming PC, Wii U, 3DS
