It wasn't the most prolific announcement but it's one that made tons of fans happy today. Metroid Prime 4 is being developed for the Nintendo Switch.
"Metroid Prime 4 (working title) returns to the first person adventure roots of the original Metroid Prime game and introduces a new storyline that ties together the events of the Metroid Prime universe and takes the storyline in new directions" according to series producer Kensuke Tanabe. Tanabe is leading the project together with a talented new development team, and they are hard at working bringing the actions, isolation, and exploration of the Metroid Prime universe to life on Nintendo Switch.

Given the super limited reveal today, there isn't any word yet on when you might actually see this game get released. I wouldn't expect it for a while though.