I remember watching this show when I was a kid. I rewatched it again a few months back and I was instantly hooked. The characters are pretty likeable, and there's this one comedic character that I know most of the fans would find annoying, but personally I really like him. Most of the characters have character development, but I do wish that two of the main cast, Kord and Trixie's character and backstories were explored more. Other than that, I love the interactions and relationship between the main cast.
The story is really good for a show that was made to sell the toys. It seems kid friendly enough with positive messages and familial themes, but it's also filled with darker themes as the story goes on and I enjoy it a lot. The show has incredible world-building, it's action-packed and the slugs and other creatures are all unique. The main villain for the first few seasons is really interesting and well-written, the main villain in the latter seasons was also good, and more terrifying.
My main gripe with this show is one of the characters (that was sort of major since he was mainly affiliated with the main villain) just disappeared after a small appearance in some episodes in the earlier seasons and the main villain for the movie Into the Shadows, whose origins, in my opinion, doesn't make much sense. Still, the show's really good, amazing story, good characters, and the movies are really good too (aside from one of the villain's origins). It's a shame the show was cancelled and the last movie they had kinda ended on a cliff hanger.
I hope the show could be renewed for another season or two, or maybe a final movie as a proper goodbye to the franchise. I hope this review was helpful to those who want to try watching it. It's an underrated gem and I highly recommend it.