New stuff I learned before I started to play Pokemon Shield, thanks to Austin John

1. The Starters are shiny-locked so we'll have to get Shiny Starters from DLC or events like we did with Shiny Lunala. (I never liked Shiny Lunala anyways, she looked like a pile of sick.) Don't know if you can soft reset for IVs or if they are always just the same IVs no matter how many times you soft-reset to discourage you from save-scumming.
2. Shiny Pokemon won't appear like they did in Let's Go, you have to fight them to see if they are shiny like in the regular games, which is good because I like the surprise.
3. You will be able to toss your old Pokemon for better evolved forms of the same thing with better stats in later areas. This was a common thing in all Pokemon games but these games strongly discourage grinding and EV training and want you to GET ON WITH STORY!
4. Tech Machines which you can use over and over again are joined by Tech Readouts, which are TMs that follow the old-school one-use-only creed but have insanely powerful moves. It's unknown whether you can only get one per game but you buy them with Watts which is a currency you get by slaughtering or capturing Pokemon which glow gold. You might wanna catch the golden Pokemon though as they have 31 IVs in at least two stats, making them great for competitive battling.
5. The Name Rater, Move Deleter and Move Rememberer are also now one person, a fat lardguy who is in the Pokemon center. This is very convenient. Also, traded Pokemon are no longer safe to be called Pikachu and Corviknight, because if the trader didn't give them a nickname, this guy can change the nickname of a traded Pokemon. However, as I said, it's only done IF the traded Pokemon kept its original species name, ie the trader didn't nickname his Pokemon. With the option to turn off the option to nickname Pokemon as soon as you catch them, this feature is very useful indeed. :)
6. Heart Scales probably no longer exist in the new generation as the Move Remembering doesn't cost a Heart Scale anymore, you can learn Level 1 moves for no cost! This will make that Moonblasting Gardevoir so much easier to get. ^_^
7. Hidden items are hidden no more - they will glitter at their spot. Also, like Ni no Kuni 1, these glittering items respawn every so often so you can farm them for items like Repels and berries.
8. If you want to trade with yourself, you can do that as soon as all of the major tutorials are over which takes about thirty minutes. Once you meet Professor Magnolia and leave, you are now able to trade Pokemon with friends... or a second Nintendo Switch since you can't trade on your save files. :(
9. You also get a fishing rod. Yep, if you really want to have a Gyarados, you can get one before even leaving your hometown!
10. Once you leave town, you'll have to go through the Wild Area, which is the selling point of the game. This place is filled with lots of high-level Pokemon but you can avoid them easily. This is why I doubt a Professor Oak challenge will work here as you'd have to capture all of these Pokemon before stepping foot in Motostoke City.
11. Of course, you will quickly find that a Professor Oak run is undoable here due to the game being a jerkwad. The gym badges no longer not only prevent you from playing with traded Pokemon over the level lock but also prevent you from throwing Pokeballs at a high-level Pokemon. Because the levels in the Wild Area are very random, they level-lock you so you get an error if you try to use a Pokeball on a "strong-looking" Pokemon saying "There is a time and place for everything, but not now! Run away!!!!" All you can do is defeat the Pokemon, but it'll respawn after an hour of real time or something. You MUST clear gyms and fight their Dynamax Pokemon in order to lift level locks. I assume this is because Game Freak was sick of people buying two games, speedrunning one and then letting their other game breed up new Pokemon in the other game.
12. After you beat gyms, the Wild Area Pokemon will grow quickly in level, so don't expect that Zigzagoon you met at Level 3 in the first visit to be Level 3 when you return after winning the game, it'll be Level 100 and a strong-looking Pokemon and will one-shot your in-game team. You'll start running into fully evolved Pokemon as you clear the story. This is sort of like the MMO aspect of the game to ensure you don't spend your entire life in the Wild Area. ;)
13. The Pokemon Dens in the Wild Area are useful. The ones without light shooting out of them will give you a lot of Watts, but the ones that shoot light will let you enter a Max Raid battle with a Dynamaxed Pokemon. You don't have to do this online; if you enter without selecting help, the game generates NPC trainers to help you out but their AI is as dumb as a Rhyhorn's, they aren't here to help you win just to help you survive. None of them will Dynamax, so you are expected to do the honors. The raid ends after ten turns have passed without any defeat or the Dynamaxed Poke wipes out four Pokemon on your side. It can be four of your allies' Pokemon so be sure not to let them get killed.
14. Sadly, the Judge Function that lets you check IVs on your Pokemon is, like in Generation 6, post-game only so you'll have to go do online calculated guessing if you want to know what your Pokemon's IVs are.
15. You will get berries, stardust, TRs and lots of candy from winning a Max Raid(either by capturing the Pokemon and killing it, but you probably get more rewards for catching it), there are experience candies that give set amounts of EXP and you can even get Rare Candies! The more stars of difficulty a raid is, the better the prizes, so you will have to be Max Raiding a lot to get any profit from it.
16. Unlike normal catches, Max Raid catches are 100% successful, any Pokeball you use will act like a master ball. It's like the Let's Go mechanic of legendaries and tough foes requiring you to kill them before you can catch them only you don't have to worry about them breaking out. Guess that Game Freak has small mercies and didn't want you to bite your arm in rage by having this giant maijin break out and beat you up every time you fail a catch. ;)
17. To counter these small mercies, you don't get any EXP from Max Raids, but you'll be getting candies that give set EXP so it's not a big freaky deal. ;p

See you guys in Galar! ^_^