Ninja Turtles: The Next Mutation is a flawed attempt at reviving the green team after Power Rangers overshadowed it and became the popular children's heroes. Made by Saban Entertainment, the same company behind Power Rangers (and therefore, the company partly responsible for TMNT's downfall, other factors being the horrible third movie and the fact that the Turtle train ran out of steam, resulting in a drop in quality for the toys and cartoon), it's an okay attempt at a live-action Ninja Turtle series, but sadly, it is a flawed one.
The series is a loose continuation of the New Line films (therefore, we have the subway lair seen in the second and third film, and Splinter is still missing an ear). However, with this one, there is no April O'Neil or Casey Jones to be seen (although it's been said the two would appear had the series gained a second season). The heroes-in-a-half-shell are now 18-years-old in this show and are in for new adventures along with a new female Turtle, Mei Pieh Chi, a.k.a. Venus De Milo, a Shinobi apprentice (which in this show, Shinobi is another word for chi magician). Shredder is there, but only for the first two episodes, as he is defeated and replaced by a new villain named Dragon Lord, an evil dragon who leads The Rank, a group of dragons who were imprisoned by the ancestors of Venus' sensei, Chung I. Other villains used are all exclusive to this series, and that includes Silver, a yeti who is a crime boss, Dr. Quease, who is basically the show's Baxter Stockman, only he is into studying mutation, and Simon Bonesteel, a big game hunter who hunts and sells endangered species.
So, with this series, it is live-action with suit actors (like in the New Line films). However, the editing is poor, as you can see the suit actors missing stuff and a scene where Mikey accidentally touching Venus' chest in one episode due to the suits not giving much vision. Also, Saban make a lot of continuity mistakes in the series (like the controversial dialogue where Leonardo tells Venus the four Turtles we know and love are not really brothers). Plus Venus herself has been a controversial character. She is basically a fish out of water who uses "Shinobi magic" and her main thing is getting sayings wrong (like calling the Turtles' home a toilet and Raph correcting her that it's sewer).
Those flaws were enough to turn many TMNT fans away. The reason for its cancellation is conflicting, with official sources saying the ratings were not good, with another source saying Saban pulled the plug due to the show being expensive to produce and as Fox Kids did not own the TMNT franchise, they did not make any money from merchandise sales. From there on, the story continued online, however, when Kevin Eastman sold his share of the franchise to Peter Laird, Venus and all the other characters introduced would be erased and locked away, never to be used again (even as a joke, as Kevin Munroe would say in an interview for the 2007 TMNT film). While this is okay, the flaws do detract this show from being great, but I believe characters like Venus and Simon Bonesteel should be used in future series, especially if they were given improvements to fix the flaws this series showed.
