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.
This aspect of his character comes across strongly in "Rub-a-Dub Sub," where Louis goes fishing and one of Mazarin's men hooks a dead fish onto his hook so he'll catch something. During the scene, he acts confused, but later in the episode he acts annoyed and practically states outright that he knows exactly what they did.
Fanon: The official website's bio of Siroc identified him as a former slave, but this piece of information never appeared up in the show. The most popular fanon explaining Siroc's backstory — detailed in this fanfic — makes him Cardinal Mazarin's slave.
Growing the Beard: The first two episodes played up the comedy with over-the-top situations, cheesy dialogue, and anachronistic references. Beginning with the third episode, the dialogue and acting noticeably improved, the plots focused more on fantasy and drama with a bit of comic relief, and the anachronisms were underplayed (with Siroc's role as the inventor becoming more about angst than comedy).
Ham and Cheese: Much of the cast, to varying degrees. D'Artagnan starts off as this in the first couple of episodes, but mellows out after that.
Hate Dumb: Young Blades aired on PAX, known for its wholesome shows with Christian overtones. Shortly after the premiere, people started complaining on the PAX messageboards about how evil and anti-Christian it was to have a show featuring an ambiguously Satanic cult. Nevermind the fact that the leader of the cult was the show's unambiguous villain and the cult was immediately established as evil.
Shipping Goggles: Jacqueline/Siroc shippers interpret a few ambiguous facial expressions Siroc makes in "Da Vinci's Notebook" as evidence that he's in love with her.
They Just Didn't Care: In "Rub-a-Dub Sub," it's understandable why the sacks of gold were filled with plastic coins and not actual coins... but you'd think someone would dub over the noise of obviously plastic coins clinking together.
D'Artagnan's hair extensions. There's pretty much no effort to hide the ends of Tobias Mehler's actual short hair under the ponytail.