If you know the Avatar series, the adaptation doesn't do it justice.
We see no character development. Katara has no personality or hope. Aang is not child like and wanting to have fun. Sokka isn't sexist towards katara or sukki. Zuko is shown being nice and you feel bad for him, when the original series you aren't on his side at all. Azula isnt perfect and intimidating and we never see Azula until season 2 in the original series. Also firelord Ozai is shown a ton when in the original series we barely know about him. And Aang isn't swoon by Katara.
Things that were totally different from the original series were how Aang wakes. The artifact to Ko. No pirates. Sokka and Katara in the spirit world. Visiting the waterbending avatar kyoik at the north pole. Princess Ueya not being betrothed and showing up as a fox in the spirit world. How Aang finds out how the moon spirit will be killed. Princess Azula in season 1.
The way they pulled in things from the original but changed it like how they meet jet(sokkas instincts tell him to walk the forest), the spirit world, how they visit omashu (ride the mailbox system), why they visit Keeoshi island (ride the oonagi fish), meeting the mechanist and his son (in the air temple), meeting king boomi (tests were to know his name and he basically was trying to kill Aang in the remake), not knowing flopsie, how they get the waterbending scroll (Katara steals from pirates), how they have the Appa whistle (Aanga buys from market not automatically just has it on the first episode), who figures out Aang is the avatar (Zuko tells but gran gran tells in the series), no pirates, Aang not learning from Katara or Master Paku how to waterbend, Hann and Sokka getting along (they don't get along at all), how Uncle Iroh truely gets caught (he is in a hot tub rock), it was altard so much that it doesn't follow the same storyline really which left me wondering why change it even with limited time. They might as well just made up new characters and said they can bend the elements. So much was altard from the original, and it leaves out key info.
I probably left out more changes, but this remake changed so much about the characters and story from the original series that I didnt enjoy it.