Wilfred Nagel...

Nagel already thought he was a "god" for having perfected the serum; he didn't need to take it to be satisfied with his work.

Also, it wouldn't have mattered to the plot if he had taken it (indeed he might have done so); Zemo surprised him (all of them) with that bullet. Supersoldiers aren't bulletproof at close range, and I'd guess Zemo would know how to execute a kill shot even if Nagel HAD taken the serum. Dude's unstoppable, which is why we love him.

Bucky's "ah" seemed to be both confirming (why is the gun not shooting, "ah" it's empty) coupled with his growing annoyance with Sam and combat in general.

In fact, one of my favorite aspects of the show was Bucky's behavior in combat -- never afraid, of course, because he's an ex-HYDRA assassin and a cyborg supersoldier, but never cool and collected either. His overall attitude under crisis seemed to be aggravation.

Bucky's annoyed/disgusted expression as he and Sam flee Selby's goons cracks me up every time.

Also loved his attitude while fighting the Dora Milaje -- patient as a parent until Ayo took his arm, the only time in the series he actually looked shocked (as well as betrayed)

Now Zemo, THAT's cool and collected. Except once. One of my very favorite instants is when Walker's getting all impatient, waiting for Sam to reason with Karli. We get a couple quick shots of Zemo watching Walker closely with what looks like shock and worry. If the "U.S. Agent" should lose control again, I'm guessing the Baron and his butler will take him down right quick.