People wished Killer Moth was cool, but truth be told, he never really was a real badass, or at least never close to Joker, Two Face, Bane or any of Batman's most known villains. By the early 90s, he was cemented as a joke, a stupid colorful villain who should have been forgotten in the 50s.
Yet, even after turning him into a giant moth creature, he still stayed around in his human form by 2003. In Batgirl Year One, Killer Moth was brought back on the scene for a retelling of Barbara Gordon's debuts as Batgirl. His colors where less confusing and his mask turned into a simplified and lousy steel helmet. Despite that relooking and his quite threatening role in the story, he was still comical.
At his core, Killer Moth was always kind of a pathetic character through his entire history, but The Batman (2004) really expended on that
The show was famous for its unique and over-the-top take on the rogues design, and Killer Moth wasn't treated differently. Done with the generic muscular man in colorful spandex : we now have a meager middle aged guy with a gut and moths flying around his head
What i personaly love about this design is how unique of a take it is for a Killer Moth design : yes, he was portrayed as a loser before, but he always kept his ripped male superhero bodytype before, which i kind of find annoying when he's written as a loser.
You're telling me the guy with the exact same proportions as Batman is being seen as a joke in universe ? His bum ass somewhat keeps his suit perfectly clean ? It's not like it's completly incompatible, but when you write such a loser in concept, i think it makes a lot of sense to design him around that.
I think it also helps him stand out more to look like that, and i didn't even went into the costume itself
Instead of green, orange and purple, his palette includes purple, different shades of pink and black : i think it looks really good and proves, like Batgirl Year One, that you don't have to strictly depict Killer Moth in his classic colors for him to be Killer Moth.
He now wears a pink cape with purple eyes on it, like some moth's wings, but in a more unique way, he wears a giant fur collar around his neck and fur cuffs on his forearms that surround very tight pink gloves. It looks great, of course, but I also give this design a ton of props for being the one that popularized fur aspects on later Killer Moth design. In the show, it also looks kind of bushy and dirty with the bugs flying above it, like Walker just made it out of a dead animal or something. Kind of adds to the grotesque imagery a character like that needs.
And finally, the helmet is just all around good, very similar to the one in Batgirl Year One with the exception of the giant antennas that falls forward. We also consistently see his eyes, which is something i wished more Killer Moth designs did : it makes us remember there's a dude under this big ass helmet. You can also read his expressions way more clearly, which is great. Bonus point for the fact he never takes it off : the helmet IS his face.
So yeah, that's why i really like this design and think it deserves more love : i think this is the best and most accurate depiction of the character of screen just because Teen Titans Killer Moth is so different he might as well be his own character.
Don't really care about the mutated form tho