You're right, this thread should be moved to /1ntr/.
I would definitely recommend classic Ben 10. The sequel series Ultimate Alien Force and Omniverse, they're mixed bags and while I like both for different reasons they go in some wildly different directions. But Ben 10 classic is a 10/10 show, pun not intended.
Anyway, It's an entertaining and creative sci-fi series about a kid travelling with his cousin and grandpa around America in an RV during Summer Vacation, except Ben finds an alien watch called the Omnitrix that lets him turn into any of ten (At first, he gets more over time) 'Superpowered' aliens, though the 'Superpowers' are normal for that species. I like what the original series did there, it's something its sequels forgot when it introduced usual capeshit stuff like superpower-stealing machines and superpower-negating devices and a villain who somehow gets powerwanked and nerfed at the same time. The sequel shows are mixed bags.
I don't want to spoil the great shit the series comes up with, but it comes up with some great shit.
Each of the classic Ben 10 aliens are well-thought out, interesting, and balanced. No shark-jumping "This guy is an Omnipotent universe-buster and these guys are lolsorandom jokes" bullshit here. And even though Ben can choose any unlocked alien and turn into it, The Omnitrix will often give him the wrong alien, forcing him to think on his feet. Plus, sometimes weird shit will happen to the watch or Ben, screwing with what he ends up getting.
My personal favourites out of all his aliens (Even counting sequel-show stuff) are the classic aliens Upgrade and Grey Matter.
Upgrade is a blob that upgrades and controls technology it touches and Grey Matter is a shoe-sized smart guy.
If I could recommend just one episode from this show… Season 1, Episode 7. The episode that introduces Kevin.
Another really underrated thing about the show? Grandpa Max. Not as great as Uncle Iroh from Avatar, but he's up there.