"Trollhunters" was conceived and brought about by Guillermo del Toro - a name to conjure with in cinematic circles, although I'm unlikely to ever forgive him for "Pacific Rim." He conceived of this as a TV series, but ended up writing it as a book first. It was picked up by Netflix, and so we have an animated modern urban fantasy kids coming-of-age tale (with lots of trolls). The first season has 26 episodes, each roughly 23 minutes.
The series opens with two trolls fighting under a bridge in Arcadia, California. The evil Bular (voiced by Ron Perlman, a frequent del Toro collaborator) triumphs over the noble Kanjigar (voiced in the first episode by Tom Hiddleston, and in all other episodes by James Purefoy (yes, despite his death)), but Bular loses his prize when Kanjigar chooses to step into sunlight which turns him to stone. What Bular wanted was the amulet of Merlin - which calls to high school student Jim Lake (Anton Yelchin), who rescues it from the pile of rock that used to be Kanjigar. He assumes the mantle of "Trollhunter" rather involuntarily, the first human to ever have the title. We find an entire world of trolls hidden in caverns under Arcadia (and apparently the entire world) unknown to humanity. Jim and his best friend Toby Domzalski (Charlie Saxton) find themselves being tutored by the troll Blinky (Kelsey Grammer) and befriended by the immense but charming AAARRRGGHH!!! (Fred Tatasciore). Eventually, their fellow student, Jim's friend and potential love interest Claire (Lexi Medrano) is brought in as part of the team as well. After all, her little brother has been replaced by a changeling (referred to as "Not Enrique" and voiced by Jimmie Wood, he's actually a fairly major character). They have to contend with all the usual high school crap while also contending with evil trolls and bad magic.
Jim Lake is an unusual character in a kid's show: he's well-adjusted. His home life isn't perfect (his mother is so busy as a doctor he takes care of her more than she takes care of him, and his father left the family when he was five), but for the most part he's a decent student, neither a nerd nor a jock. The show moves along briskly, with all kinds of twists and turns. Some characters change sides (the only "sides" that matter here are "good" and "evil"), but I felt like their reasons were less arbitrary than they often are in TV series (kids or not). The teacher Strickler (Jonathan Hyde) was particularly interesting: he's definitely mostly evil and one of the team's primary enemies, but has surprising redeeming features and consistent goals that make it all make sense. They also sprinkle in occasional adult jokes and a variety of adult overtones that the kids won't get (but won't be deterred by either). My personal favourite in this category was the naming of a gnome - he starts out as a nameless pest, but Toby manages to befriend him and names him Gnome Chompsky. Which is hilarious to kids because he has nasty teeth and chomps, and hilarious to adults for other reasons.
Wikipedia points out that "Filmlink's Travis Johnson" called the series "... the best children’s animation to come along since Avatar: The Last Airbender." High praise indeed: that was pretty much the best kids fantasy show ever. I'm inclined to agree, with the caveat that Avatar is still the better of the two.
At 26 episodes, this season is too long. They filled it out with a reasonable plot, but ... still too long to get where they were going. The next two seasons are 13 episodes each and I think I'm going to prefer that.