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.
YMMV: X-Wing Series
Complete Monster: Ysanne Isard is Director of Imperial Intelligence and Emperor in all but name. Along with the traditional things that come from being at the head of the Empire, like oppressing nonhumans and ordering strikes against the Rebels, and what she did to the previous people in power, she ordered the creation of the Krytos Plague, which causes infected nonhumans to die horribly, and set it loose on Coruscant before the Rebels captured it. This so that the New Republic would both bankrupt itself trying to treat the infected and tear itself apart along species lines, as resentment towards immune humans rose. It might not have gotten that bad, but that was the intent. And then there's how she left Coruscant. And Lusankya. At one point, Wedge thinks to himself that Isard might not have been evil on the scale of the Emperor or Darth Vader - aside from Luke and sometimes Leia, few people in that 'verse consider Vader anything but evil even after his Redemption Equals Death - but that was small comfort to the millions who died at her hand.
Crazy Awesome: What the Wraiths come up with when they're working together (for example, the Lunatic plan, which gets them from floating helplessly in deep space to hijacking an Imperial warship). Lampshaded numerous times by Wedge.
Wedge: Wes, they're doing it to me again.
Janson: Yub, yub, Commander.
Ensemble Darkhorse: Tycho Celchu. Stackpole didn't know he would become so popular when he created him. And in a way, Wedge Antilles, who has a small but devoted set of fans. There's also Wes Janson, who was offscreen for the first four books, reached this status incredibly quickly when he replaced Tycho as Wedge's "on-screen" second-in-command and brought the funny with him.
Janson: Performing a puppet show while flying is a felony on some worlds.
Harsher in Hindsight: Isard's Revenge (published 1999) has several rather eerie parallels with the Iraq War: a highly controversial invasion of a neutral power to depose a dictator for political reasons, publicly spurred on by supposed evidence of a bogus superweapon.
Wedge proves he can be one, when he teaches Falynn a valuable lesson about respecting her superior officers, and when he plays an epic prank on Janson involving the entire crew of the Mon Remonda. Plus the plan he uses against Isard at the end of Bacta War.
Throughout Solo Command, we get to watch the plan unfold that makes one of these out of Nawara Ven.
Airen Cracken, too, given his scheme in the first three books to try and prove whether Tycho is a sleeper agent or not by giving him Emtrey and allowing him to discover the droid has functions that would be useful to a spy. Not surprising considering the Imperials consider him to be Isard's Rebel counterpart.
By the time Mercy Kill rolls around, Garik Loran has well and truly earned the title. No one, not even Voort, could have seen two Wraith Squadrons coming.