Anyone have suggestions as to a similar cartoon?

Hm, it's not exactly what you're looking for, but you might enjoy Courage the Cowardly Dog. It's got the weird and creepy tone down pat. While I was watching OTGW I was reminded of Courage a little bit. It's episodic though.

I think the movie Coraline has a similar feel to this mini series. The music is amazing too in that movie as are the visuals. Trailer---> https://www.youtube.com/watch?v=Js7wxoqeVK0

Also, I know you said shows and movies but I will recommend two books which are "The book of lost things" by John Connolly and "The Thief of Always" by Clive Barker. They are both books about children/a child who wonder through a wonderous land/house that is not as it seems. Kinda like Coraline (which has a book that is good too).

Someone tasted my tongue and told me I tasted like the color crimson with a faint of violet. 

Gravity Falls! I'd say Miyazaki films but you didn't want anime... Old Disney fairy tale films I guess. Perhaps old Tim Burton movies like Edward Scissorhands? Just search for dark fairy tales!

Where The Wild Things Are?! That's about a kid that goes to another world, sort of. Maybe Narnia, if you're into that!

It's hard because there really isn't anything like Over The Garden Wall which makes it so freaking awesome! I would love more shows or movies like this.

Maybe Corpse Bride, Last Unicorn, Secret of NIMH

This is kinda like anime but kinda like not, but look up the movie "Mind Game". It's extremely nonsensical and uses a very weird hybrid art-style, but there's something oddly appealing to it like this show, and while it doesn't make sense most of the time, everything slowly ties in together at the very end.

But really, I just finished watching this series and if anyone else knows of one like it.... :[ it was so good.

I'm not much of a videogamer, but OTGW reminded me of a couple games I've played: "Bioshock Infinite" (which has a similar turn-of-the-century kind of nostalgic vibe, both in its graphics and story) and "Monument Valley" (which has similar ghostly, slightly melancholy music, and a lead character proudly wearing a cone for a hat).

As for animation that has a similar aesthetic -- OTGW owes a debt to Windsor McKay, which you should check out. It shares nothing at all with Lotte Reiniger's work, but Reiniger's silhouette animation has a similar old-fashioned charm. Check out "The Adventures of Prince Achmed."

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I should warn you -- he's a Fourierist.

Here are some suggestions, I'm sorry if I accidentally included titles that were already mentioned. (95% of these titles can be found online, you can message me if you want links)

Like other people said:
Ernest & Celestine (one of my favorites)
Amazing world of Gumball - I know you disagreed with it but give it a chance it has a some of the same zanyness and randomness as OTGW
Fullmetal Alchemist
The Monument Valley Video game was awesome, and kinda similar

Other suggestions (I know you said no anime but nothing else that is current (2000s and later) really comes close):
Natsume yuujinchou
Oblivion Island: Haruka and the Magic Mirror (Movie)
Summer Days with Coo (Movie)
David the Gnome
little nemo adventures in slumberland (movie)
Howl's Moving Castle (also a book by Diana Wynne Jones)
The Black Cauldron
The Golden Compass
The Princess Bride

Honestly movie-wise it reminded me a bit of Labyrinth. There's also a print comic out there, had short story-arcs, Thornwatch - some vague similarities but it didn't have quite the whimsy and innocence OTGW had.