I have mixed reactions to this.
The blink dog: Dislike the removal of keen hearing and smell. This change really seems to me to be one of many that are basically designed for VTT play at the expense of flavor and world building elements.
Moving the teleport to a bonus action, I really like.
The bugbear: I HATE changing goblinoids to Fey. This is a change for no reason that I can see. It is one of the only places where WotC is actually inserting lore, but it's intrusive in that it changes long established lore in a way that has mechanical consequences. Yuck.
Removing Brute and Surprise Attack are changes I don't see the purpose in- the poster of the video theorizes that it's to remove passive, always on abilities, but I don't see the point of this. Adding the Abductor trait is... okay, again, why? What does that have to do with bugbears and their traditional depiction? Feels like another change for the sake of change to me. The weird damage on the hammer is just weird, and seems very arbitrary.
The bullywug: I like moving its ability to jump to a bonus action. I don't like the removal of swamp camouflage; again, loss of flavor for the sake of VTT integration is not something I care for.
Also, I am not a fan of giving them a rapier in place of a spear. That, again, removes traditional flavor in place of a weapon that is, in my opinion, kind of advanced technology for a bullywug.
The mage: Medium or Small is good. Improved hps seems misguided to me; mages should be squishy. Arcane Burst is... God damn do I hate this ability. It removes any tactical advantage from closing in on the mage, is an ability that pcs can't get, and is an example of the overuse of force damage in the new rules.
I'm okay with the changes to the spell list, given the inclusion of Arcane Burst, but I'd rather have the old version of the mage. I think the notion that we wouldn't see Greater Invisibility cast in combat is pretty wild; with no other real concentration options for the mage, it seems like an obvious choice to me for round 1.
I do love that they include Counterspell and Shield in the reactions section; I've been doing that for years.
The sprite went from a "not great in combat" creature to a "gonna hit and gonna hurt" type of creature. I think we need more stat blocks for things that aren't great in combat. I also definitely prefer the old sprite's sleep poison for the sake of tradition.
The worg: Not a fan of the changes. Again, removing the keen senses is... I don't see how it's an improvement.
The change to the bite from maybe proning you to granting advantage on the next attack against you seems weird. I mean, wolves (etc) taking creatures to the ground is a real thing, and I think it's a shame to lose it. Again, there is a subtraction of flavor in favor of simplicity. I don't need that, but I dunno, maybe the majority of dms do.
The warhorse: I'm glad that Trampling Charge moved to the Hooves action; it makes it harder to miss how it works when running it. The reducing of the damage, I like less so, but you know.
The bullywug bog sage is cool, though I do wish it still had the Swamp Camouflage ability.
FInally, he talks about the shambling mound without having access to the new stat block. I like everything he said here except for the addition of lightning damage. On a variant version of the SM? Absolutely, very cool. But for the baseline creature, which hasn't ever had such an ability? Meh.
I guess maybe a big thing for me is that changing stat blocks so much really effects the tactical setup of encounters from older adventures. I fondly remember a bullywug and titanic toad adventure I wrote where the bullywugs' swamp camouflage was a key element in, well, probably at least four encounters. I know you can arbitrarily throw in the equivalent of it with advantage based on the terrain or whatnot, but having it explicitly in the monsters' stat blocks is (I feel) far better.
Anyway, those are my thoughts... I continue to be not really impressed with the overall direction of the new rules, even if they seem mechanically sound.
