Rockman.EXE/MegaMan NT Warrior is one of those series which was modified fairly heavily in transit to English, 4Kids-style... but to tell you the truth, that doesn't make a huge difference, as it's a pretty heavily Westernized Saturday-morning-cartoon style anime by design. 90% of the changes in the English version weren't for content. In fact, they don't seem to be for any reason at all. But I digress. This review covers both the Japanese and English versions (which, again, the difference isn't as huge as other examples).
Writing: The storyline somewhat follows the plot of the first two Battle Network games (of which this series is based off of)... eventually. Truthfully, it pretty much skips over the entire first game, as the first half of the series has a very cartoony, episodic, adventure-of-the-week structure to it, with the WWW agents from Battle Network 1 given wackier personalities and made the proverbial Team Rocket of the series. Fairly typical for a Saturday morning kid's show, but not exactly a shining beacon of ingenuity in terms of writing.
The second half of the series enters into the plot of Battle Network 2, and does a somewhat faithful job in following the storyline... with the exception that most of the Gospel navis' operators never make appearances (I guess implying that they're all standalone navis) and that a rather large plot element was changed at the end of the story which eliminated one character entirely. But compared to the first half of the series, still a relatively faithful effort.
Now, I could go on about the many silly changes made from Japanese to English, but this being a Saturday morning cartoon sort of anime, that much is kind of a given. What's really silly is that they made changes from the English versions of the games, which were themselves already changed in transit--I can only guess this had to do with ease of animation, which would explain how Mayl became "Maylu." Gives me Lamu flashbacks. Anyway, while most modern dubs are quite faithful adaptations, this is not one such case--entire episodes are cut from the English version, so the only way you're really going to get the whole story is in Japanese. Of course, if you don't care too much about the story (you're not missing too much) and just want a fun, nostalgic cartoon ride, either version is perfectly suitable--and it is pretty fun to hear Light Yagami barking orders at MegaMan. ...oh, and Mr. Match's accent is pretty awesome, too.
Art is fairly typical for the type of anime this is. It's meant to be pretty simplistic and Westernized, and... well, it succeeds. There's really not a whole lot to say here.
Sound, I also feel I've pretty much covered already above. None of the voices are ear-grating in either dub of the show, but you're not likely to be blown away by any heartfelt performances, either.
In all, the series as a whole is a fairly mediocre one with low production values and a very Western target audience upon inception. It's a pretty toyetic show which the producers didn't feel the need to expend a lot of time, effort, or resources on, and it shows. If you're looking for a great anime series with a strong storyline, well-developed characters, and brilliant plot twists, you'd best go elsewhere. If you're a fan of the Battle Network games, like me, and the thought has crossed your mind that "Y'know I bet it'd be kind of cool to see this series animated," feel free to give it a watch. It can be fun for nostalgia purposes, but doesn't hold a lot of water on its own merits.