Florence Pugh was excellent as Yelena, with perfect comedic timing and some subtle emotional work. Her heartbreak at realizing that she's the only one who considered their fake sleeper cell family real (or so she thought, anyway) was very affecting. I'm eager to see more of her in the MCU -- I guess she'll be turning up in the Hawkeye series. It remains to be seen who or what Elaine represents, but it's probably nothing good; it seems Yelena went from being a pawn of one shadowy organization to another. Sad, and probably the result of her hunger for belonging.
I would have liked more Taskmaster action; she had a real Terminator/Winter Soldier vibe going there for a bit, but then she dropped out of the movie for a large chunk and became more tragic than menacing once the mask came off. (I like that they spun out a throwaway reference from The Avengers into a whole subplot, though.) If I were better at unpacking fight choreography I would probably have recognized a lot of moves from previous films, but broadly I saw references to Cap, Hawkeye, T'Challa and Bucky. And Natasha, obviously.
David Harbour's Russian accent kept drifting in and out, and I don't know how much his being Red Guardian added to the proceedings. Really, it's just another wrinkle in the increasingly messy history of the super soldier serum. Whatever, it's fine.
I had heard a rumor that RDJ was going to cameo in this, but apparently not. That's fine, there wasn't really a place for him here that wouldn't have felt like a gimmick. Nice to see Secretary Ross again.
Assorted quibbles:
I have no idea how Taskmaster tracked the vials from Budapes(h)t to Norway. I guess they really are training super spies over there.
Why were S.H.I.E.L.D. scientists working under a front? They were an official government organization. (Maybe that question is really naive of me.)
I love a helicarrier, me, but the Red Room turning out to be a gigantic flying fortress was a bit much.
Could one Widow really bring down a nation, or was Dreykov just cribbing from the Winter Soldier sales pitch?
Why does Natasha think she still needs to break the other Avengers out of prison at the end? I guess Civil War's final scene took place a lot later than it appeared. Or she's just not up on current events. (I liked the Avengers theme sting, though.)
Something doesn't sit right with me about Elaine twisting the events of Endgame to goose Yelena into killing Hawkeye. He was the only one to come back from Vormir, so his version of events is the only version, official or otherwise. How does Elaine spin that to make him look responsible? Or if she doesn't have to because Yelena is just that eager to avenge Natasha, wouldn't she have gone after him already anyway? I'm probably overthinking this.