Not sure what to expect, but I hesitate to apprehend that they'll send us an E3 for their first year of a console and leave us utterly disappointed. Therefore, my rating is 7...
The main game is Super Mario Odyssey. Hopefully, Nintendo can somehow imitate and fuel BOTW levels of hype for this game (preferably more) and therefore justify the purchase of a Switch in the holiday season. The Galaxy games acquired variety and charm, so Mario Odyssey ideally should have a mixture of the recency of Mario games in terms of level design, but the gameplay mechanics of Mario 64, all in a sandbox setting. I have a hard time believing a contemporary Mario game could receive unprecedented levels of hype- but this is a Nintendo game, and they did it with Galaxy, so they could definitely do it again provided the effort. I guess I'm influenced by the disappointment of 3D World to presume this game can't turn tables.
As for other realistic expectations: Xenoblade 2 (apparently delayed tho?), Pikmin 4, Retro Studios (new project), Fire Emblem Warriors, Fire Emblem 2018 (unless strictly 2017 titles), Project Octopath Traveler, SMT 5, MarioXRabbids, MHXX localisation, Skyrim (?), short indie showcase, short third party showcase, BOTW DLC...
If this is truly a spotlight, then we could expect a mention of 20 games in 25 minutes, following the last Direct, remembering this isn't a conference. So we could be very well in for a treat. Hopefully, that doesn't include any more Mario games other than Maker however (please no Mario Party or sports games). I don't expect ARMS as they have already shown that game to death. It will be playable at the show floor but it has no place in a spotlight (it will only show up if Nintendo has literally nothing else to show). I have a gut feeling we'll see Splatoon 2.
As for those surprises specifically, Nintendo couldn't have ignored the Mother 3 outcry (E3 2014, anyone?) and the constant Smash pleading by fans...Animal Crossing sentimentally echoes as a 2018 title...since the last release was almost 5 years ago! They have to dish out E3 with at least one surprise, as the fans are literally who keep them afloat, so listen...