(TL;DR): Even without the context of the original cartoon, this adaptation has a "college project with a high budget" vibe, like they were in a rush to get it to their professor's desk on time. All of the acting, writing, choreography, and cinematography is mediocre at best and cringe-worthy at worst. The VFX are better this time around at least, but they rarely utilize it where it was needed most and ultimately doesn't outweigh it's shortcomings.

The CGI is way better than the 2010 movie, but all the hurdles that come with live action still plague the Netflix show. They cut a lot of really good scenes because they'd be too hard to animate, (like Aang's escape from Zuko and subsequent first use of his avatar abilities) which creates a lot of pacing issues, and what they didn't cut is plagued by awkward writing and even worse delivery.

Everyone has something missing from their original character that was a key characteristic in the cartoon. Aang is always super serious now, which shows in his fight scenes too and overall removes the whimsical nature of the show... All of the characters in general are now super serious, so the show is pretty devoid of any lightheartedness... Zuko is a lot less measured and he comes across as silly, which is ironic because he's the one character who's supposed to be very serious... Sokka doesn't start out sexist, which removes an entire growth arc from his character and takes away a key dynamic between him and Katara... Iroh doesn't have his iconic wise/disciplined enigma vibe... I could go on.