The Shrine

Release Date Announcements
* Rabbids vs. Mario RPG (XCom Style) August 2017
* Fire Emblem Heroes September 2017
* Super Mario Odyssey October 2017
* Xenoblade Chronicles 2 November 2017

New Game Announcements
* Metroid 2 Remake for 3DS was just announced with a trailer and treehouse demo (as I am writing this)
* Next Mainline Pokemon on Switch
* Metroid Prime 4
* 2D Sidescroller Kirby Switch
* Yoshi platformer for Switch
* Rocket League announced for Switch

Flagship Game Key Details
* Super Mario Odyssey core gameplay mechanic is essentially Space Station Silicon Valley on Steroids, you can use your hat to possess a bunch of different enemies, and flip out to become Mario again. This game also looks to incorporate Link Between Worlds style wall merging, except it turns into classic style 2D Mario gameplay - enemies can transfer into the 3D world as well. It looks like a worthy Galaxy/Mario 64 successor.
* Xenoblade Chronicles 2 is unrelated to Xenoblade Chronicles or Xenoblade Chronicles X, but looks heavily influenced by Faxanadu and Skies of Arcadia, while not specifically shown, the Zohar looks to be making an appearance. There's a character that looks heavily based on Albedo in it.

So the format Nintendo is using is a bit different, they kicked off with a Spotlight Nintendo Direct which really didn't spend much time on any particular title. Then they are expanding on what was shown in that Spotlight during Treehouse events throughout the rest of the event. They are also announcing new titles, showing new trailers, and showing gameplay for the newly announced titles over the next three days. The first of these was Metroid 2.

Metroid Prime 4 is not being developed by Retro Studios. This has upset some some media sources and Metroid Prime fans; but this is largely because they don't understand that Retro Studios 2017 is not made up of the same developers that made up Retro Studios in 2002. The expertise and experience is completely different. Yet there is this weird failure in logic causing the belief, by some fans and media, that not only is Retro Studios capable of developing a Metroid Prime game, but that they are the only studio capable of developing it correctly.

In short, the majority of the Metroid Prime team has been gone for 10-15 years.

Retro Studios formed in the late 90s with much of the Turok Dinosaur Hunter and Turok Seeds of Evil staff, they began working on a bunch of different projects that didn't go anywhere. Nintendo was looking for a team which specialized in developing first person shooters, as this was an incredibly popular market on the N64. The team who had specialized in Turok games for a half a decade seemed the best candidates, and they gave them the highly regarded Metroid license, and they worked with Shigeru Miyamoto on Metroid Prime; a game that many regard as a masterpiece by the American studio, but not without its toll. Retro Studios has always been a small studio, and to get the first Prime game out the door it took 80-100 hour work weeks. In 2002 Metroid Prime released for the Gamecube. Retro would develop two more Metroid Prime games over the next 4 years, and during this time most of the original staff left the company.

Due to the lack of personnel, Nintendo switched Retro Studios over to focus on the Donkey Kong Country series. They are currently working on an undisclosed title, and I believe it is most likely a new Diddy Kong Racing title. My reasoning is that Super Mario Kart 8 Deluxe is already out, and assuming Nintendo is going to stick with the 1 Mario Kart per generation strategy, they'll have a big gap. By 2019 there's space for another Kart game. Retro Studios has been collaborating with the Mario Kart Devs since Mario Kart 7. The other possibility is that they're working on an original franchise, and have filled new staff positions for the project.