Kinnikuman Nisei ("muscleman" second generation) is a sequel to the classic Kinnikuman series, which was a spoof of the superhero genre (think Ultraman) in which superheroes and villains are all wrestlers. The show as a whole is as ridiculous and over-the-top as it gets, and it's clear from the get-go that the series is intended for kids. The show's main gimmick is that the protagonist, while usually a total goofball, becomes an incredible wrestler whenever he gets into a pinch. As stupid as he is, it's fun to watch how he grows both as a character and a fighter to surpass his "spoiled royalty"-type personality and become a respectable person. Now, comparing the new series to the original, they're virtually indistinguishable from one another, with Nisei basically being a "same show for a new audience" type of deal. What makes the new series more of a sequel than a reboot is that many of its characters and enemies are the direct descendants of characters from the original Kinnikuman, hence the title "second generation". For that reason, while the anime and an off-shoot manga series were aimed at children, the main manga series was published in the Japanese Weekly Playboy magazine, finding a readership among those who grew up with the original. If you ever watched or read the original, you know exactly what to expect from this one.
As for my personal opinion, there are some inspiring moments here and there, which make it worth the watch in the long-run (this goes for both series), although, other than the concept, there's nothing particularly special about the show, which unfortunately says quite a lot, because the humour is something that only children will mainly enjoy. Animation is decent: character models are surprisingly solid and seem to stay consistent throughout the series, although not all scenes have top-notch animation, since the fights are usually dragged out to cover a couple of episodes. That being said, for a basic shounen anime from 2002, I found it to be better than worse. What really kills the show for me is the protagonist. I've always said to people that what makes or breaks a show for me are its main characters, and I personally can't stand shows where the protagonists are constantly making a fool of themselves, like Dumb and Dumber, and Kinnikuman/Nisei are no different in that sense. It's really satisfying to watch this type of character learn to be respectable in moments of need, but you'll find that those segments are few and far between: for every minute of the series I enjoyed, there were a few that I just weren't that interested in. So make sure to keep this in mind when deciding whether or not to give either series a watch. Ultimately, they're stuffed full of innocent fun, and I believe it's worth watching an episode every now and then if you're ever craving something elementary, but it's not a series I would consistently indulge in.
Now, it wouldn't be a full review if I didn't mention the English dub, which was handled by 4Kids Entertainment and completely reworked for Western television under the name "Ultimate Muscle: The Kinnikuman Legacy". The original series never made it over to the west, hence the name change, although figures and merch were released in the region under the name "M.U.S.C.L.E.", so the show's new name reflects both of its Japanese and Western roots. 4Kids' dubs are known for changing the feel of the show by injecting a different style of humour that's more directed at western youth. This, along with the fact that all of their shows are edited/censored to meet the standards of the Fox broadcasting network, is the reason that many anime fans dislike the majority of their work. In the case of Ultimate Muscle, however, the changes do little to damage the series. Heck, because the series is so over-the-top to begin with, the comedic changes have been said to sometimes actually better the show as a whole. I haven't watched much of it, so I can't actually give a solid recommendation, but from what I've heard, the dub is quite funny, and the show was so popular in the West that the final season of the show was actually a separate series that 4Kids requested be produced specifically for the Western market. How cool is that? Anime fans will feel comfortable watching the original Japanese version of the show, while the dub definitely feels more juvenile, a little more like a Saturday morning cartoon. If you just want something to laugh at, go with the English version, which doesn't seem to take the story very seriously at all, adding in a lot of extra humour on top of the original script. For those who want something more shounen-esque, meaning it has deeper story-telling moments sprinkled in with the humour, than watch it subbed, but be warned: it's very difficult to find the entire series in Japanese with English subtitles. The dub is a lot more widespread online.
In my books, an anime is a must-watch if in the 90's, worth watching if in the 80's, casually enjoyable if in the 70's, and not a complete write-off if in the 60's. At a 70/100, I'd say that Kinnikuman Nisei--or Ultimate Muscle, whichever version you decide to watch--is a fun show that will take you back to your early days of watching Saturday morning anime, although, even in that context, this one just barely makes the cut. Yeah, it's fun, and Kinnikuman is a classic, but there are definitely better shounen anime out there. At the very least, I think you'll enjoy the few episodes you watch, even if you never choose to go any further with this one. As for me, I'm on episode 8 or 9, and although I don't plan on continuing it any time soon, I'm not ruling out a future viewing of another episode or two. It's just that kind of show.