Alright, so here's the short version of my opinion:
- Better than the Nicktoon, much better than the Fred Wolf cartoon, subjectively better than Rise but has more objective flaws.
- Adaptation is about as good as can be expected given the target audience, aside from obvious liberties.
- Starts a little wonky but gets better in the first season, quite satisfying throughout seasons 2-4, 5 is weird and 6-7 just devolves it into a generic action cartoon.
To be more elaborate I think the other Turtle cartoon it's the most similar to is the 2012 Nicktoon. Now the latter largely aimed to do the same thing, rework a bunch of old TMNT material into a coherent storyline. The main difference in approach is that the Nicktoon picked whatever to rework (arguably a little too much from the Archie/FW versions) and ending up straying so far you wonder why they even bothered looking into older material, while the 4Kids show exclusively either took something from Mirage's comics or made up something new. While the difference in terms of adaptation could be argued, it's more important to discuss the actual quality of the shows themselves. On that note I think the 4Kids show has a much more clear direction, most plotlines were finished to some extent and it rarely ever felt like you were just watching filler, while the Nicktoon moved along in a bizarre and somewhat repetative manner. While neither show had a very high budget, it's pretty clear that the Nicktoon was much more restricted by it as they often ended up forcing the characters to go back to the same locations over and over again, while the 4Kids cartoon never really had that problem. I realise that's because of the difference between traditional animation and CGI but it is still a noticable problem.
Comparing the show to the Fred Wolf is basically pointless. FW TMNT was essentially a bad comedy that only adhered to a bare minimum of faithfulness to the source material due to contractul obligations, a major character like Casey only appeared to market his toy and that's it. As adaptations the 4Kids show is clearly the more faithful show. In terms of quality the 4Kids shows wins by the default, as it was made in a time when blatant animation errors wouldn't pop up every five minutes in every episode, it's absurd how awful 80's cartoons can be. The 4Kids show knows how to keep the scripts well paced, while the FW show struggles with filler scenes in a sad amount of episodes. The FW show is pure garbage, the only fair comparison is to TNM and that show is literally only worth bringing up to point out there's technically a worse TMNT show than FW.
When it comes to comparison to Rise, I have somewhat mixed opinion. Subjectively my problems with Rise is that it's simply not what I want from TMNT, the 4Kids show is a much closer representation of that. The 4Kids is simplt the better adaptation, while Rise pretty much only does it's own thing. On the other hand I can't say the 4Kids show is objectively better, since it has animation and storytelling problems I simply don't see in Rise.
And now (finally) I get to wheter or not the 4Kids is a good adaptation. Is it a good adaptation by any normal and reasonable standards? No. About half the episodes of the first four seasons have nothing to do with the comic and even the ones that do have rather drastic changes. There are also changes that seem rather arbitrary, such as making the clearly human villain an alien. Then by the fifth season, any similarity to the comic has been dropped. What we have to consider though is that it's an adaptation that is:
- Meant for a younger target audience than the comic.
- Part of a franchise that to this day has very few even remotely accurate adaptations.
- Based on an american comic (by default those almost never get faithful adaptations).
- Partially funded by a toy company.
With those factors considered it is (somewhat sadly) the most accurate adapation of Mirage Studios TMNT we'll ever get. Now some changes aren't really bad though. I would be a fool to deny that the comics didn't have some very big flaws, these include presenting the events in a somewhat bizarre order and leaving things unintentionally vague. Such problems simply ought to be adressed. In terms of the arbitrary changes, I'll have to admit I don't really mind them but they do cause a drop in accuracy points. Still, this show does still score more of those than most others so far...
As for the show's quality aside from the adaptation aspect... Overall, I like that the storyline keeps going throughout the first 5 seasons without ever getting derailed too hard is something the other shows haven't accomplshed yet and I give it props for that. It's mainly the thing I enjoy about the show, that it could tell an ongoing storyline. There are examples of good action but most of the animation tends to look a bit cheap, though they do seem to be a bit smart in trying to relegate the cheapness where it isn't as noticable. Like all the other shows there's toy marketing involved and I'll always hate that stuff, really takes you out of the show and reminds you of the cynical reasons the show actually exists. It's the absolute worst of it is in the early episodes season 1 where the plot really does take a backseat to show the Turtles skateboard or some crap. To their credit though, the blatant marketing is toned down throughout season 1, they tried their best to actually weave the toys into the story in an organic way and they were often destroyed if they had to market something similar in later episodes.
The big problems do start in season 5 where they stop adapting stuff and takes the show in various bizarre directions. By the final season, the show had simply devolved into a generic action show. The story was basically non-existant by that point and the toy marketing was once again in full swing. They also changed the tone of the show which was not appreciated.
In conclusion, there are problems with it, there definitely are. However, it is one of the few kid oriented versions of TMNT that has something to do with the source material, and it's a lot better written than the other TMNT cartoons. If we keep getting versions that are worse than it, that would make me sad.