For what it's worth I did not like Green Lantern: The Animated Series.
The set pieces were largely uninteresting and unoccupied. There was an odd sense of emptiness to the show, like it was lacking extras. I imagine this is due in part to no one wanting to develop 3D models for random characters. It was especially noticeable when compared to the comparable Clone Wars, which had huge battles with loads of troops and vehicles, and cities populated with inhabitants.
The art style wasn't to my taste. I'm not going to say it was bad, I'll just say I personally found it off putting.
I felt what the showrunners REALLY wanted to focus on were their original characters, Razor and Aya, and I believed this undermined the lead character, Hal Jordan, who didn't have much of an arc compared to those two. This is a problem Hal Jordan faced during those Johns years. He's in the midst of action, but he's only there to be in action and he doesn't really have any character arc. Johns wanted to world build Corps and Entities, and the animated series was more interested in Razor and Aya, yet Hal Jordan is supposed to be the main character.
I didn't like the depiction of Anti-Monitor or Krona. There were better templates to use right in the comics and the show chose to do something dumber instead.
Somehow the musical score felt canned and cheap. It went for a John Williams Star Wars vibe, but...maybe the synth voices weren't the best choices, but somehow it just didn't come together well for me. This kind of exacerbates the emptiness problem mentioned above and the weird art style, and all-together, the show had a kind of cheap-ish vibe to me. The weak intro in general probably doesn't help. I know it was made in 2011, and things maybe changed a bit by then, but the intro to an action cartoon should really get the viewer pumped, like Mega Man:
I know the GL show is very popular with its fans, but it wouldn't surprise me if there wasn't all THAT much interest in it. You just...of course wouldn't hear from the people who weren't all that interested in it. Granted, that's just me saying something. I don't have graphs to show how popular the show was, but yeah, it didn't get resurrected and Young Justice did.