I would say the Super Mario 3D All Stars collection, or the GTA Trilogy

Definitely Metroid Dread. Went in with little expectations after Samus Returns, but the game is a superb Metroid experience through and through, fully modernized and quite the looker. It looks GORGEOUS on the OLED screen.

I honestly have a couple big positive surprises.

1) Xenoblade Chronicles 2: I did not own a Wii U (initially, I did buy one a few years after the Switch) and I was not in a good position to buy new games when the original came along. When they announced and showed of Xenoblade Chronicles 2 I thought I'd give it a shot, since I heard such good things about the other games. For the first ten or so hours I was actually bored and I thought it just wasn't a game for me, then it just clicked and I was absolutely hooked. It took me a long time to beat the game due to work and school, but it's absolutely one of my favorites for Switch, and it helped me buy both Xenoblade Chronicles 1 and X as well.

2) Ring Fit Adventure: When this game was announced (just dropped out of the blue if I recall correctly) I thought "Oh, of course. Nintendo is being Nintendo. This will drop like Labo). Months after it launched I didn't really hear about it. Then the pandemic hit and I couldn't go to the gym anymore. My girlfriend saw the game and really wanted it, so I was able to pick up the very last one at a store for Easter (this is when it was notably hard to come by). I thought I'd try it and give up on it and let it be her thing, but I've sunk so many hours into that game, and I still have more to do. I've only stopped using it because I'm now incredibly busy with both work and my graduate degree, but I cannot tell you how great of a workout and game this is. It's much better than Wii Fit in pretty much every way, and my only complaint is with the joycon disconnections and not the game itself. Even then, it's very rare for me.

3) Metroid Dread: I have to admit, I was never great at 2D Metroid games. The first Metroid game I ever played was Metroid Prime 2: Echoes and I really enjoyed it. I tried to get into the other games that weren't part of the Prime series, but I just wasn't good at them. I purchased Samus Returns for the 3DS, and didn't finish it. I just had game ADHD and kept switching to other things, then I'd come back and have no idea where to go. Metroid Dread not only influenced me to go back and play the entire Metroid series again and beat each and every 2D game, but the game itself is absolutely phenomenal and really gives me hope for the Metroid series as a whole. So far sales look fantastic, and I hope this is the much needed boost in both quality and sales that fans of the Metroid series haven't had in well over a decade.

Nothing I guess, though that's probably because I've only played maybe five different games on the system. BotW, Mario Odyssey, Luigi's Mansion 3, SSB Ultimate, and Mario Kart 8 and they were all more or less in line what I expected in terms of quality.

Doom 2016. This was the first 'impossible' port and proved that even high-end PS4/XB1 games could come to Switch and run well. Witcher 3 and Crysis will never match the surprise of the first one to do it.

For me, probably Metroid Dread.

I went in expecting a 7/10 game to pass the time, but it ended up being one of my top Switch games.

I think what surprised me the most was that I expected the difficulty to be frustrating, but while it was a tough game, it had a similar quality to Retro's Donkey Kong Country games, where even when I died it was like "okay, one more try, I bet I can get it this time" and rather than getting pissed off I just kept coming back for more, as the eventual victory felt so damn good.

I also didn't expect its pacing, level design, and progression to be so insanely satisfying. Reaching new areas, gaining new powers, and somehow always ending up right where I needed to be was like a constant dripfeed of pure dopamine. 

Phenomenal game.

Ring Fit Adventure was another. It made me realize how much I really like surprises. This one just kind of popped out of nowhere. And it must have surprised a lot of people because, while it launched to a relatively low level of sales, it’s now become Switch’s big sleeper hit.

I have to add Animal Crossing: New Horizons to the list. While certain elements of the game had a sandbox approach, they’ve really expanded that in this version of the game. Now it is one of the most successful single platform games in console history - I believe it’s now the fifth highest of all time, only after Wii Sports, Super Mario Bros, Mario Kart Switch, and Mario Kart Wii. That was a massive surprise.

While Breath of the Wild is my favourite game on the console and easily one of the best games of all time, I can’t say this surprised me. I saw this one coming way before we even knew it was going to be a Switch game.

Previously, the only Metroid games I was able to really get into were the Prime trilogy. Those I consider some of the best games ever made, but 2D Metroid just never clicked for me before, and I loathed Other M.

Mercury Steam also have an inconsistent track record.

Not truth at all, Zelda I agree, but Xenoblade Chronicles is on the same level. And I'll take Pikmin 3, xenoblade chronicles 2 or monster hunter rise over mario odyssey. Even tough some are ports, but Xenoblade looks way better than the wii version and pikmin is a more unique beast, most people never had a wiiU, in fact around 95% of the people who own a switch never had a wiiU, so pikmin 3 was like a brand new game for the vast majority.

Animal crossing did more for the switch than zelda too. And I believe the next big game will be pokemon arceus.

I can only dream of a Mario Galaxy 3 before the generation is done.

Those other games you mention, stardew, fire emblem are really nothing special, they're just good games that's all, I wouldn't buy a switch just for those games.

Also thought about it, but New Pokemon Snap. Pokemon Co is not really....known for doing something that the fans actually want, and a sequel to Snap is one of those 'Oft requested' titles.