I didn't really the like the way in episode 1 Katara from the original series was just like "yea, my brother and Aang are dead" like it was nothing, she even seemed happy about it; and the way it was done narratively is a big no no in comic story telling. The original series took its time telling the entire story over 3 whole series whilst this one seems to just be rushing into it.
Plus everything seems to be a joke to everyone, even the serious characters... one of the things i liked about the original series was how some of the characters had those hyper-comic faces when they were "unimpressed" or "angsty" and even if a bad person had to act cartoonishly goofy (Mai/Ty Lee) they were only in out of context "moments". But now everyone seems to do that all the time; the bad guys, the good guys, the old guys, the extras... it's hard to get a read on the different characters when they're all acting *finger quote* "goofy".
I liked the original series because it wasn't just a child's story, but this just feels like a typical modern nickelodeon cartoon. "wahoo, look at all these whacky larger than life characters".