The biggest of the big.
Probably the single biggest news story of the year came early in the morning of St. Patrick's Day, when everyone in North America woke up to the news that Nintendo had entered into an agreement with DeNA to create a new account system... and mobile games.
It forced late Nintendo president Satoru Iwata to reveal the NX codename far earlier than they perhaps planned, and was scheduled to release this fall until being delayed at an October shareholder's meeting. We learned there that Miitomo is more of a social application than a game, and would have free to start elements.
It wasn't the biggest game to open with, but as a staking post for the new Nintendo, Miitomo is definitely one of the biggest newsmakers of the year.
#4: The Legend of Zelda Wii U
It's amazing that a game that showed approximately ten seconds of footage in November can be one of the biggest newsmakers of the year. However, like Emperor Palpatine or Ganon himself, it was always in the background hanging over the rest of the year.
We were coming off the high of the footage at the 2014 Game Awards, but March 27's delay of the game set events in motion that set up Star Fox Zero, then Mario Tennis Ultra Smash as the holiday title. By being delayed just after the NX announcement, rows upon rows of speculation were written about a possible Twilight Princess situation where the game would come to the next console (whatever that is). Not bad for a game that still doesn't have a title - but we KNOW it'll have amiibo support.
#3: Super Smash Bros (Wii U / 3DS)
A lot of the amiibo craziness of 2015 was caused by Sakurai's announcement last year that every character in Smash would have an amiibo, but a couple of fateful announcements in April kept the hype train going for last year's releases going into December. By confirming Lucas's return and giving fans a suggestion box for ideas, it drove a year's worth of downloadable additions, but even the people voting for Shrek never expected who would choose to settle it in Smash.
Smash added some old friends this year - Roy, Lucas and Mewtwo - then added Ryu complete with classic control options at E3. But the biggest news came in November, with the introduction of Cloud Strife. Adding one of the characters most identified with Sony to the Nintendo competitive action game was seen as a betrayal or a moment of curiosity by some, but cemented Super Smash Bros as a series celebrating video games in general. The year ended with a stunning upset, as Bayonetta triumphed in the ballot (among characters available) to be the final addition to the roster.
Congratulations to the Smash team for keeping the hype train rolling all year, and now go and rest our heroes.
#2: Pokémon Go
When the Pokémon Company announced a "major partnership", nobody could figure out what it would be. And literally nobody predicted that it would be Nintendo and the Pokémon Company teaming up with Niantic - a former part of Google - to create an alternate reality Pokémon game in the style of Ingress.
The possibilities were endless for what bringing Pokémon into the wild like this would do, and there was clear demand - Pokémon Go was one of the most searched games in the world all year, beating out the likes of Madden, NBA 2k16 and Bloodborne. And although it's technically not a Nintendo project, it was one of the last projects Satoru Iwata locked down before his passing in July. Now, can it come out so we can start diving under trucks looking for Mew?
It wasn't just the quantity of news that made Splatoon #1 - though it was the first game to really get the firehose of content that would later be used in Super Mario Maker.
It wasn't the game being a runaway success - though it's sold about three million copies to this point and become the first shooter of the first or third person variety to sell a million copies in Japan on consoles.
Splatoon is #1 because it marks a change in how Nintendo is going to handle console development. Nintendo held a beta for the first time ever (the Splatoon Global Testfire) and marketed the game like no new series they've launched since Pokémon. By letting the Garage go and create something brand new and getting behind it, Nintendo's created a demand for a franchise that will definitely be around for the long haul.
The future is going to be bright for Nintendo following the low of the Wii U, and Splatoon is going to be a major part of it. That's why Splatoon is the biggest newsmaking game of the year.