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.
"Funny Aneurysm" Moment: Raimundo's throwaway line in "Chameleon" (season 1, episode 6) - "Maybe I'm missing the point. We're never gonna go after each other!" Talk about Tempting Fate.
GameBreaker / Story Breaker Power: A few of the Wu fall arguably fall into this either on their own in unique combination. The first notable one was the Golden Tiger Claws, allowing the user to essentially invoke Teleport Spam and make any Showdown a breeze. It was even sent to the center of the Earth for a while so it wouldn't be used.
The second item was Treasure of Blind Swordsman, which required Raimundo to fake a Face Heel Turn and scam Roy Bean since direct methods were out of the question.
News that the revival is being outsourced to Canada is already getting this reaction.
Jack's new voice—with a higher pitch that makes him seem a lot younger—is also getting this reaction (though it was later revealed that it was simply a place-holder since his actual voice actor hadn't been hired yet).
Fans also seem to be objecting to the use of CGI in the Showdowns, and the seemingly random name change to the Orb of Tornami, called the Orb of Torpedo in the preview clip.
The name change is actually justifiable. The names of the Shen Gon Wu are still the property of Warner Brothers, and so their names will be changed slightly or else the new show won't be able to use them.
Most of these, however, were from a preview that was, as confirmed by the creators, leaked and not supposed to be on the internet in the first place, they also stated that it's also a fairly old clip; it's extremely likely that it's going to change somewhere down the line.
Villain Decay: Jack Spicer and Wuya, as both were upstaged by Chase Young, although Jack wasn't all that tough to start with, and Wuya was restored without her full powers. Even then, she can still beat all of the monks.
Reversed in the first part of the finale, where Jack's future self pretty much kills everyone.
Villain Sue: Chase Young borders on this at times. He's powerful, intelligent, handsome, highly skilled, outclasses every other villain on the show as well as most of the heroes, and almost never suffers major setbacks either.
The Woobie: Jack Spicer, and sometimes Omi and Raimundo.
Kimiko, big time in Tangled Web.
Dojo in Master Monk Guan what with being the butt of everyone's jokes, called out for not helping the monks fight Jack's Wuya-Bots even though they've always known he's not exactly brave and he almost gets killed so Chase can use him as a soup ingredient.