These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Awesome Music: Trocadero really gave Jeff Williams a run for his money this season, and the song that appears during the credits "Contact" really brings home the emotional core of this season.
Harsher in Hindsight: Church and Carolina's decision not to say goodbye at the end of season ten to make it so they're "just not here right now" was initially portrayed as heartwarming, but it turns out Tucker and Caboose are both hurt by Church's disappearance.
Awesome Ego: Felix. He's got a bit of an ego, but there's no denying he's badass and many fans love him.
Base Breaker: Felix; many fans think he's a Mary Sue, others find him fun and entertaining. It depends on how you feel about the most badass member of the Resistance being voiced by the writer of the season, who would, by extension, be responsible for the perceived badassery of him.
Ensemble Darkhorse: Every named Lieutenant in the New Republic army got instantly popular after the first episode. The most popular by far seems to be Jensen; being the first prominent female character who wasn't constantly pissed (besides Sheila/Fylis and Sister, at least, and not counting Kimball who was introduced first but her characterization wasn't clear until after Jensen), being incredibly Adorkable, and voiced by a popular Rooster Teeth personality all probably help with that.
On the flip side we have Emily Grey who's with the Federal Army of Chorus who is already steadily gaining popularity. Doyle seems to be exempt from this, though.
Harsher in Hindsight: In the trailer, Tucker's response to Kimball wondering how they'll win the war if they can't even rescue a few prisoners is, "We'll wing it." His attempts at winging it in his first mission end up getting most of his men killed.
Tucker leaves Pamolo as a look-out because he believes having him on the field will get everyone killed, an assessment Pamolo agrees with. By episode's end, Tucker's deviation from the plan has led to the deaths of his other two men.
One-Scene Wonder: The 'Why Snowman?' guy is super popular with a lot of the fandom.
Caboose was originally written in just to balance out the teams after the Reds got Donut, and then as a catalyst to annoy Church. But as Caboose grew more and more stupid (and more and more lovable), he soon became probably the most popular character.
Grif's Deadpan Snarker attitude led to an increase in his popularity among fans.
Wash, despite showing up six seasons in, is one of the most popular characters on the show. His backstory makes him quite the splash with female fans, and he's probably the fandom bicycle.
Dude, Not Funny!: The joke in the "Best Ever of All Time" DVD about Donut being sent to some sort of institution for being/acting gay/feminine was met with this reaction. It's understandable considering it's rather dark and in rather poor taste.
Best shown in the Recollection with Wash, who ends up imprisoned in Reconstruction before being betrayed by Meta after the two have teamed up in Season 8.
Another example in Season 8 (again) with Tex, who ends up caught in a capture unit and then wiped from existence by Church Things would likely have turned out differently had she not tried going on a Roaring Rampage of Revenge.
Another great example in Season 10 with Church and Carolina, who almost end up dead and eventually declare it isn't worth it after seeing a broken down Director.
The Woobie: Due to his childlike personality, Caboose gets a lot of sympathy for suffering that the show generally inflicts on its characters.
Church gets pretty well established as this (well, as a Jerkass Woobie) once his backstory is unveiled.
Agent Washington's life is tragedy, plain and simple. Got a lot better after the Recollection trilogy, though.
All the guys have their moments when you just want to hug them like Simmons in Season 4 and 9, Tucker in Season 11 and 12, and Grif when he's being shot at.