Super Smash Bros. Ultimate
Smash is back in a big way with Super Smash Bros. Ultimate. It will have every fighter from every Smash Bros. game including Ridley from Metroid (see the video above).

You can use a Game Cube controller and all Amiibos can be used.

There are also some changes and tweaks to the mechanics that you can learn about, along with everything else about the game, in this 25 minute video: https://youtu.be/L93H7YC-83o

Super Mario Party
This one is interesting. A bunch of new, fun looking mini-games as you'd expect, but this one brings in extra functionality if you use multiple Switches. The downside being that to use it, you need multiple Switches but still. It's neat. This one feels like it really bridges the gap between the Switch as a handheld and the Switch as a home console.
https://youtu.be/7pu9t5AL1Ss

Fire Emblem: Three Houses
I've never played a Fire Emblem game so I'll rely on comments to tell me how exciting this announcement is. The trailer shows what looks like a really pretty and very capable turn-based strategy game. I got real Valkyria Chronicle vibes from this which is a good thing for me.
https://youtu.be/rkux5h0PeXo

Other tidbits
Those three are really the big ones, but there were more announcements. These stood out for me

  • Xenoblade Chronicles 2 is getting DLC: https://youtu.be/-EP6XV1BmOk

  • Fortnite and Hollow Knight are out now on the Switch. Soon, you'll be able to play Fortnite on Amazon Echo I bet.

  • Octopath Traveler has another demo out now