I see this as the first episode in which Brotherhood really begins to diverge from the '03 anime. The episode begins with one of my favorite characters from Brotherhood.
And there goes this Basque Grand, which is fine by me. I didn't like him very much in the '03 anime, so cheers to his early demise. Plus, I am a bit biased towards Scar.
Beyond this point though the episode ranks as FMA's more depressing episodes. I think that can be said for both versions of the anime.
Introducing this episodes creepy evil guy with squinty eyes drawn to make him look like a loving father figure. He reminds me a lot of Cornello at this point. This was never a connection a made until I started pulling screen shots and writing this stuff up, but both Tucker and Cornello start out looking sweet and relaxed with their eyes closed. As the episode progresses and we see more of Tucker's dark side, his eyes gradually open, and the lighting in his scenes gets darker, much like it did with Cornello. The only difference is the timing. Cornello goes evil fairly quickly, while Tucker takes most of the episode to show his true colors.
All these fun scenes with Ed, Al, Nina, and Alexander. They're bright and cheerful. They really want to make you love these guys.
The eyes are starting to open. Clearly the happy times from the middle of the episode are not going to last...
The eyes are wide open now, and he's going on about how what he did wasn't really that wrong because science. Yeah... No... This was a great idea, said no one ever.
And the end of Tucker and Nina. In the '03 anime, Scar only stumbled upon Nina. Here he has intentionally tracked down Tucker. He ends both of them here.
At this stage, I remember wondering where the story would go as both Basque Grand and Tucker played larger, although still secondary, rolls in the '03 anime. It might be worth adding here that I have not read the manga, so all of this was entirely new to me the first time I watched through it. I found it quite exciting, as I especially disliked the Lab 5 episodes from the original anime, and without Tucker they would clearly change.
This episode plays on what I think are two of FMA's major themes: the value of human life and ethics in science. Ed is greatly distressed by Nina's transformation and loss of humanity, and then, in spite of what Tucker has done, Nina still loves her father and values his life, which she demonstrates when Ed attacks Tucker and again after Scar has killed Tucker. And, although there is some justice in Tucker's death, there is only sadness for Nina and Alexander. Their deaths feel cruel and wrong. This episode sucks... period. It introduces Scar, and sets up themes, but overall still leaves a bitter aftertaste.