This might get long...
As always I recommend you look at reviews or a video to see if the game would be for you first.
The Must Plays:
Dead Cells: You said you like roguelikes? This is one of the best.
Super Mario Odyssey: This is just a no brainer. One of the best games on the system.
Super Mario 3D World Plus Bowser's Fury: It might be worth it for Bowser's Fury alone, but if you've never played 3D World on Wii-U, then it's a must buy.
Super Smash Bros Ultimate: It lives up to the title. I keep wondering if they'll release a version with ALL the DLC on disc, but this is a must-buy.
Pokemon Legends Arceus: Probably the most interesting Pokemon game. Plus, good news! You can actually catch ALL the Pokemon in this game with only one game. No trading is required.
Metroid Dread: Definitely try to find this one. It's hard, but one of the best (and only) Metroids we've gotten in years.
The Xenoblade Saga (Xenoblade 1 Definitive, Xenoblade 2, Xenoblade 2 Torna Golden Country, and Xenoblade 3): All of these RPGs are a good time. And you can play them all on Switch! (Except for X for some reason, but maybe someday). I'd probably recommned starting with the first one.
Hyrule Warriors Age of Calamity: This is a prequel to Breath of the Wild, but it's recommended you play this AFTER you finish Breath of the Wild. It's a Dynasty Warriors styled game. There's also Hyrule Warriors Definitive, which is more of a crossover between all the different Zelda games. Age of Calamity has a better story. But Definitive is also fun.
Kirby and the Forgotten Land: You might scoff at a Kirby game, but this is arguably the best Kirby game we've ever gotten.
Luigi's Mansion 3: This game might just be perfect to play around Halloween.
Sonic Mania Plus: Arguably the best Sonic game we've gotten in a decade.
Monster Hunter Rise: A lot of people are falling in love with this game.
Ori and The Blind Forest/Ori and the Will of Wisps: A couple of gorgeous platformers.
Teenage Mutant Ninja Turtles Shredder's Revenge: This is already out digitally, but it's getting a physical release soon. Maybe the best TMNT beat em up ever? There's also the Cowabunga Collection collecting a bunch of TMNT games coming out soon.
Shovel Knight: This is one of the biggest indie platformers ever. I say go for it. Eventually.
The Solid Buys:
Super Mario 3D All Stars: This might be getting hard to find. But, it collects 64, Sunshine, and Galaxy 1. Definitely worth getting. Might depend on if you've already played them all, though.
Super Mario Maker 2: It's heyday is probably behind it, but it's still fun to play around with.
Mario Kart 8 Deluxe: With all the DLC coming, this is probably worth it even if you did play it on the Wii-U.
Animal Crossing New Horizons: It depends on if you like these life-simulation games. But, if you do this one's pretty addictive.
Stardew Valley: Another farming/life sim game. Everyone likes this one.
Fire Emblem Three Houses: One of the best strategy games you'll find. If you like this, there's also Fire Emblem Three Hopes, a Dynasty Warriors style sequel.
Mario and Rabbids Kingdom Battle: This is getting a sequel soon, so maybe you want to wait for that, but this is still a really solid strategy game.
ALL the other Pokemon games (Let's Go Pikachu/Let's Go Eeevee, Sword/Shield): The "mainline" Pokemon games. There's a version of Sword/Shield with the Expansion pass included, I'd recommend tracking that one down. Legends Arceus is superior, in my opinion, but these are good too.
Bayonetta 2: A over the top action game. Bayonetta 3 is coming soon, though and MIGHT be better.
Live A Live: A remake of a cult classic JRPG from the SNES days. In a 2D-3D artstyle.
Octopath Traveller: Another 2D-3D JRPG.
Dragon Quest XI S Echoes of a Elusive Age: Do you like JRPGs? This might be for you.
Tales of Vesperia: Another JRPG.
Eastward: Another JRPG. In a more 2D artstyle.
Bravely Default 2: Another JRPG. You don't have to have played the original 2 games on the 3DS to enjoy this. This is basically a new story.
YS 8 Lacrimose of Dana: Another action JRPG. I like the island setting of this one better than YS 9, but both are solid games.
Valkyria Chronicles 4: Another Strategy game option.
Astral Chain: From the team that brought you Bayonetta.
Hollow Knight: Another tough game. But, one that most people love.
Celeste: A platformer with a surprising story.
Paper Mario The Origami King: The latest Paper Mario. It has a very unique battle system. You might want to look at a review first.
Donkey Kong Tropical Freeze: A great game. But, it can be difficult and you might have played it on the Wii U.
Digimon Story Cyber Sleuth Complete: A Pokemon like collection of 2 games.
Guacamelee One Two Punch: A collection of two Metroidvanias where you play as a luchador.
Megaman 11: It's a new Megaman game.
Megaman Zero/ZX Collection: I know you said you wanted to stay away from Megaman, but these are a little different than normal Megaman games. Also, arguably some of the best storytelling in the Megaman series. Plus, it's 6 games in one.
New Super Lucky's Tale: A charming platformer.
Yoshi's Crafted World: Another charming, if easy, platformer.
No More Heroes 3: A crazy action game. The first 2 are also on the Switch, if you never played them on the Wii, too.
Shantae and the Seven Sirens. Not as good as Pirates Curse, but this is still a really gun time. There's also Half Genie Hero out on the Switch, if you end up loving Shantae.
Streets of Rage 4: A really solid beat em up.
Steamworld Dig 2: A different kind of Metroidvania, where you're digging underground.
Untitled Goose Game: Don't underestimate this. It can be a lot of fun.
Monster Boy and the Cursed Kingdom: This aciton platformer has a gorgeous 2D artstle. If you like this there's also Wonder Boy and the Dragons Trap.
The "Maybes":
Sega Genesis Classics: There are A LOT of ways to play old Genesis games nowadays. You could even get a Switch Online Plus subscription and get a lot of Genesis games that way. But, this collection is still fairly solid.
Cadence of Hyrule: This is a different kind of Zelda game. You fight in tune with the music. You can also turn this off and it just becomes a turn-based action game.
Captain Toad Treasure Tracker: A more puzzle focused Mario game.
Axiom Verge 1 or 2: Similar to the Metroid games. These indie titles get pretty great reviews.
CatQuest 1 and 2 Pawsome Pack: Two 2D Zelda styled games for the price of one.
The Wonderful 101: A very unique game where you control a whole host of Power Rangers styled heroes.
Capcom Fighting Collection: You get ALL the Nightstalkers fighting games from the Arcades. As well as Puzzle Fighter, Gem Fighter, Cyberbots, and the rarely seen Red Earth.
Collection of Mana or Trials of Mana: Pick between getting the 3 original Mana games from the Game Boy and SNES. Or get the 3D remake of the third game in the series.
Child of Light and Valiant Hearts: Two solid indie games for the price of one.
The World Ends With You Final Remix and The World Ends With You Neo: Both are solid RPGs. The control schemes might take some getting used to, though. And even if you've played TWEWY on the DS, the Final Remix contains a True Ending that leads into the sequel.
Cross Code: Another Zelda-like action RPG. This time in a digital world.
Shin Megami Tensei V: A very difficult JRPG.
Indivisible: Action RPG with a VERY pretty artstyle.
Dusk Diver 1 or 2: A stylish series of 3D brawlers.
Flipping Death: A platformer that looks like a old Nickelodeon cartoon. Or Psychonauts.
Monster Hunter Stories 2 Wings of Ruin: Unlike the OTHER Monster Hunter game, this is more of a Pokemon-like RPG. Some people might prefer this to Monster Hunter Rise.
My Friend Pedro: Basically, a Deadpool game.
New Pokemon Snap: You're taking pictures of Pokemon. It's more fun than you might think.
Nexomon and Nexomon Extinction Complete: Do you want a harder Pokemon game with some nice 2D art? This might be for you.
The Oddworld Collection: You get 3 classic Oddworld games for the price of one.
Triangle Strategy: A 2D-3D strategy game.
Wargroove: A Advance Wars style strategy game.
Yoku's Island Express: A pinball Metroidvania.
Valfaris: A Contra style shoot em up.
Unruly Heroes: A Monkey King/Journey to the West action game done in the style of the Rayman games.
Puyo Puyo Tetris: A puzzle game with a quirky story mode.
Owlboy: Another Metroidvania.
The Longest 5 Minutes: Another RPG.
Marvel Ultimate Alliance 3 Black Order: A action RPG with Marvel Heroes.
Lego DC Supervillains or Lego Marvel Superheroes 2: The Lego games are always a fun time.
Kaze and the Wild Masks: A solid 2D platformer similar to Donkey Kong Country.
Splatoon 2: Splatoon 3 is coming soon, but this game is still solid. I'd probably recommend waiting for Splatoon 3, though.
Battlechasers Nightwar: A western RPG this time.
Spiritfarer: A unique game where you ferry the souls of the dead to the afterlife.
Zoids Wild Blast Unleashed: It's not that good, but this fighting game has giant robot animals.
Daemon Ex Machina: Again, it's not that good. But, it has giant robots.
Sekuna Of Rice and Ruin: A combination of a farming sim and a action game.
Digital Only Games:
The Messenger: A amazing ninja action game. Highly recommended.
Undertale: A Earthbound-style RPG. Protip: Don't kill your enemies.
Cuphead: It might get a physical version eventually. And it's REALLY hard. But, this action platformer is SO PRETTY.
Moonlighter: A roguelike where you run a shop.
Enter the Gungeon: A roguelike with a BUNCH of weapons.
Golf Story: Maybe the best golf game of the decade?
Donut County: A game where you control a hole. It's a better puzzle game than it sounds.
Raji An Ancient Epic Enhanced: A action game about Indian mythology.
Blaster Master Zero 1, 2, and 3: All three games are good.
Blossom Tales: A 2D Zelda style game.
Bug Fables The Everlasting Spring: Do you like the first 3 Paper Mario games? This is basically designed around those.
Death's Door: A tough action game.
Freedom Planet: A 2D Sonic the Hedgehog style platformer.
Gris: A very stylish platformer.
Dust a Elysian Tale: A stylish platformer.
Iconoclasts: A Metroidvania.
Panzer Paladin: A retro-style action game.
Touryst: A unique little puzzle action game.
Superlimial: A unique mindbending puzzle game.
Dodgeball Academia: Short of like Golf Story, but with Dodgeball.
Return of the Obra Din: You have to see this game's art style to appreciate this mystery solving game.
Scott Pilgrim vs the World The Game: A classic beat em up that you may have missed out on.
Klonoa Fantasy Reverie: Two very nice platformers that often go overlooked.
Tanuki Justice: Another fun little retro throwback.
River City Girls: Another beat em up game.
Mechstermination Force: Fight giant mechs in a 2D action game.
Cthulhu Saves Christmas: C'mon with a name like that, you MUST be curious.
Implosion Never Lose Hope: A top down action game.
Katana Zero: Another action game.
Cyber Shadow: Another ninja action game.
Double Dragon Neon: If you've never played it before, you MUST experience the best villain and ending song in beat em up history.
Clockwork Aquario: This deserves special mention as a Arcade game that was lost to time, but was resurrected due to fans wanting to find it. But...it's still a Arcade game. You'll be finished in 20 minutes.
Games you might want to avoid: Sonic Colors Ultimate (I think it got patched, but the Switch version was pretty broken at launch), Pokemon Brilliant Diamond/Shining Pearl (they're not THAT bad, but I'd put every other Pokemon game on Switch above them). Balen Wonderworld (*SIGH* Don't get me started)
I could go on, but I think you should have enough to get started.
