A charming fantasy adventure series that is pretty much unknown in the English-speaking part of the world. Which is quite shocking, given that it was a fairly big success in Japan and got 3 separate series, 2 sets of OVAs, a compilation movie, a 2020 ONA series, a 2025 spin-off (reboot?), at least 2 games, and a few distinct manga entries. The series is a cozy, family-friendly fantasy adventure in another world. The world's sacred mountain has been conquered by evil and each of the 7 layers have been cursed, so our protagonist is summoned and charged with breaking the curse on each level. There'sa broadly villain-of-the-week structure.

Each episode, the main party gets to a new town, learns how the curse effects them, and gets just a little closer to finding the tool or person they need to break the spell. An evil henchmen causes trouble, and so the mechs are summoned and they beat the villain. Around every 5-10 episodes, our heroes fight the big boss of the layer, they break the curse, and travel to the next layer. While there is an overarching story, and the characters do get developed a bit, for the most part you're intended to tune in each week and just enjoy the silly episodic plot.

The main cast is simple but well-handled. Wataru is a typical kid hero, but he's not a hothead that punches without thinking or someone that shirks away from getting things done. Shibaraku seems like he'll be the typical useless, pervy mentor, and while he is primarily a comedic relief character, he doesn't really fit that mold and is genuinely and selflessly committed to the quest. Himiko... gets endearing eventually? I don't really have an issue with her, but she's clearly the super hyper character meant to get quick laughs out of the younger end of the target audience. Most people will probably decide she's cute or annoying pretty quickly and never change their mind.

And that target audience part should be emphasized - the show is clearly intended for a young audience. It's not for literal toddlers, but it's clear they're aiming for school-aged kids and maybe a parent half-watching while doing something else. Don't expect any of the stakes to really go anywhere. If you don't find the individual episodes endearing by episode 10, then this one just can't hold your attention for another 35.

The other issue is accessibility. To the best of my knowledge, this series has never been licensed in any English-speaking country.
So it's not currently available throughs streaming services, and there aren't any English DVDs/Blu-rays floating around. You can always buy the Japanese Blu-ray sets. The first series is actually fairly cheap for imports. Later entries, on the other hand...

As for problems with the show itself, the main one is that it takes a long time to grow into itself. The first 2 layers have around a new villain an episode and most of them are forgettable or just don't work well. And some of them are just distractingly ugly. A good number of the early jokes are aimed at too young of an audience (pronunciation puns, two separate villains are bested by times tables). The main trio don't really have much group synergy or chemistry at the start.

The series irons these out steadily over time. Villains improve over the run, jokes get more character-focused or situational, and the cast gets better internal chemistry and a few much-needed changeups, but most of these end up happening around the halfway point. Notably when they finally introduce the fan-favorite rival Toraou.

Visually, the show is pretty solid. Sunrise was in charge of this one and they put in the effort. Animation works pretty well when it needs to, but it is from the late 80s. One interesting note about the character designs - all the characters are about the same height. The kids look more or less how you expect, but most adults are the same height as them or just a little taller. They accomplish this by squishing their proportions, especially cutting out most of their legs, so most of the cast look real stocky. I think it's charming, but it's not hard to imagine someone finding it off-putting. Later series don't keep this up.

The soundtrack works fine for the most part, and there are a few particular good ones, but nothing groundbreaking. The opening theme is a good fit and the ending is fun and extremely memorable.

You shouldn't expect Wataru to be really exciting or hilarious, but there's a good chance you'll endearing and amusing. It has a fully self-contained story with a conclusive ending, so it's safe to just commit to the first series before considering whether to continue with later ones.