Hello!! Earlier today I said that it's probably healthier to share threats and cores than to just dump pastes, so here I am putting my keyboard where my mouth is. So I played like 150+ battles on ladder with two different teams and I went through the Galar dex to note down some of my opinions on some of the legal Pokemon. 150 games is a large number but probably not enough to fully get a handle on a new format so I'll preface this with a disclaimer that some of these opinions could be totally wrong.
(Some other new Gen VIII Pokemon that are definitely noteworthy but which I don't know enough about to discuss yet: Dragapult, Grimmsnarl, Toxtricity, Stonjourner)
GOOD:
Braviary
This is the best Pokemon in the format for now I think. Braviary has access to the coveted Airstream / Knuckle combination which plays very well into the snowball-y nature of Dynamax in general, and Defiant just means that it's harder for opponents to stop or slow down the snowball by conventional passive means.
Gyarados
I want to speak to the CEO of Power Whip
Fossils
Fishious Rend and Bolt Beak are ridiculously powerful. Dracozolt has a better offensive typing probably—Bolt Beak is really good for stopping a snowballing Braviary or clearing up a late-game boosted Corviknight—but Dracovish has the better matchup against TR, Sand, and Rain thanks to its actually quite good defensive typing. Haven't really played around with the other two but Arctozolt looks like it could be potentially deadly on TR teams. Arctovish is probably just kind of bad. (If you're not convinced by these yet, do some calculations involving Dracovish's Fishious Rend on like Ferrothorn or Rotom-W or something.)
Rotom
I'm so glad Rotom is good again!! These basically do the exact same thing they did in BW and XY, which is burn things and stick around, but now with Dynamax they can actually do sizable amounts of damage with Max Lightning (also, for Rotom-W, Max Geyser won't miss at the most inconvenient times). With the increased viability of various Flying-type Pokemon, Electric is also a very nice typing to have (though Rotom-W needs to watch out for random Max Overgrowth from Gyarados lol who decided this was a good idea).
Sand
Sand is probably going to be the premier weather condition for this generation unless someone discovers something amazing about one of the other weathers. The already marginally-viable WP Tyranitar set got a boost this generation thanks to a few things going its way: Dynamax lets it survive more super-effective attacks; the most common Fighting-type move is now Max Knuckle, which is relatively weak; and Dynamax grants it an immunity to Low Kick because weight-based moves fail on Dynamaxed mons for some weird reason. Excadrill benefits from the drop-off in Intimidate and from having a great partner in Braviary to help snowball it even through resists.
Rain
Drednaw is a huge boon to Rain thanks to having both reasonable bulk, a solid Attack stat, and a cool secondary offensive typing; most Swift Swim users we've had in the past lacked one or two of those aspects. Head Smash is stupid. G-Max Stonesurge is also the only way I think I would consider setting Stealth Rock this generation, since the hyper-offensive nature of Dynamax in general means you don't really want to waste turns putting up SR while you get donked by an Airstream or something. Barraskewda seems kinda strong but in practice you kind of have to Dynamax it in order to get more than like one turn out of it, I think Drednaw is probably a bigger threat in general.
Whimsicott
Once the new speed mechanics go live on PS you will rue the day you said this wasn't a Tier 1 Pokemon
IFFY:
Corviknight
Having trouble figuring out how this one works. It's definitely super instrumental in some matchups (dunks on Sand teams as well as walls out most physically-biased teams) but every time I've used it it sort of just sits on the field and doesn't die but doesn't really contribute anything to the battle. I haven't tried its Bulk Up set yet so I definitely could just be using it wrong, though.
Indeedee
Indeedee feels kinda similar to a few of the less popular redirection users in previous generations like Clefable / Blastoise / Magmar in the sense that it really only sits on the field and clicks Follow Me. Indeedee has a few more tricks in Heal Pulse, Ally Switch, and
maybe Fake Out on the off-chance you're not entering the field with Psychic Terrain, but as far as I can tell it just sits there and takes hits, which makes its 70/65 physical bulk all the more worrying.
Hatterene
I don't think Hatterene is that much better a TR setter than other pre-existing options which can also put out a similarly high amount of offensive pressure like Oranguru (through its partner via Instruct) or Chandelure / Jellicent. Magic Bounce isn't as relevant as you might think since Taunt and Sleep are no longer primary methods via which to stop Trick Room from going up. Not much to say about this one, it's strong but nothing super game-changing imo.
Duraludon
I've been meaning to ask: why do people use this? Is there something I'm not getting about this Pokemon? All it seems to do for my opponents is just sit there, maybe use some non-STAB super-effective move for like 40% a couple of times, and then die. Or they spend their Dynamax on it, so it's doing 60% instead of 40%. What does this do? Like and subscribe and let me know in the comments below what this does
Sun
This strikes me as a really bizarre line-up of Pokemon to put here, but Vileplume is legitimately the strongest Chlorophyll user in the format. 50 base Speed isn't that bad when most viable Pokemon sit around 70 to 100, and the lack of viable Electric / Misty Surge users in the format (Weezing is not a real Pokemon) makes Sleep Powder spam probably at least kind of viable if you can keep Sun up long enough. Charizard is also sort of scary with Solar Power, but from what I've seen of it in play it's less threatening in practice. (Or maybe people aren't using it properly, haha.)
CBDARM
As predicted, CBCBDARM is not actually very good, but I think Scarf CBDARM is actually probably a reasonable set. In a meta where a lot of speed control comes in the form of diddly +1s from Max Airstream, and on users and allies like Braviary / Excadrill / Mamoswine / etc (which are all slower than base 95), being able to revenge kill stuff unboosted is really nice. A lot of the time it gets to trade itself for your opponent's Dynamaxed mon, which is a really good trade because Dynamax is kind of good.
Scrafty
Close Combat is a nice addition that makes Scrafty actually capable of dealing significant damage but between Dynamax providing a flinch immunity, Psychic Terrain being the only relevant terrain, and Intimidate (as of now) being a dangerous ability to even have, Scrafty feels like it got boned kinda hard this generation. Poor guy, it isn't even his fault.
Galarian Corsola
This is just kind of annoying but it's somehow a legitimate late-game win condition especially because what we have of a meta so far seems to me rather physically-biased, which is just the kind of thing Corsola likes playing against. I've only run into it a few times and most of the time the opponent just brainlessly throws it out at the start, but I think if you conserve it in the back it's a great endgame win condition to play to as long as you have other tools to stop an opposing Dynamax snowball.
Obstagoon
I haven't seen this being used well yet but I think it definitely has potential. Nice bulk overall, strong ability selection (we all know how good Defiant is thanks to Braviary), access to the now-rarer Knock Off, and a solid speed tier. Also Obstruct is actually a pretty nice move, at least in theory, in the currently somewhat physically-biased pseudo-meta.
DON'T @ ME JAKE:
Galarian Weezing
ew.