Looks like the people at the 1:21 mark know the power of Saku

I do enjoy the stamina system way more then PP. PP seemed to only really limit moves over multiple fights whereas stamina plays a much more prominent role within individual battles. This can also help make choice of what moves you want to be a lot more interesting as you now may want to have a weaker move that consumes less stamina to use between bigger attacks. The fact that you can still use a move if you don't have enough stamina (and have the difference cost you hp, and subsequently requiring a 1 turn rest) basically combines typical balancing mechanics Pokemon has used such as recoil resting after using moves such and Giga Impact/Hyper Beam rest.
Not that I'm interested in participating in competitive battles, but since the stamina bar (though not the actual number) is revealed for your opponent there could be some potential for some neat mindgames. If the opponent sees you don't have a lot of stamina may might think you won't use a big attack, but the trade-off could be potentially worth it and could create some toss up situations.
The synergy mechanic is neat as well with a move powering up in some way (whether it's more damage, higher priority, or now inflicts an ailment as well) can create some interesting switch out surprises (and combined with limited stamina could make switching out frequently a common thing).
Status effects also persist when swapping Temtem, making that doom status where it gets knocked out in 4 turns potentially iffy to deal with.
Mumbling and I have also played a bit of co-op now as that was one the big factors for me to try this out. You can basically do the whole story with a friend and that is really cool! So far though most of my issues with the game seem to be related to this currently. Hopefully they'll get the random bugs with this feature ironed out as well as change the reduced xp (not sure why that's even a thing). While co-op you can only have 3 Temtem in the party at a time (though you can change that in-between battles). I don't mind that too much as it makes you try and think about what would work best with your friend.
As Mumbling has said, this game is much harder then Pokemon. Some of it can be attributed to not fully knowing the weaknesses and such but trainers (ahem...tamers

) generally have Temtem that are higher levels then yours can sometimes rock almost full teams. Very much a welcome fact as major battles are generally won with a single Temtem remaining and feels much more gratifying to win.
The visual style works well too, nothing to complain about on that end, plus it's around half the price of Pokemon currently so it's a decent offer (and well timed considering Sword and Shield's lukewarm reception)