Some mad lads on reddit have been working for a while on remastering Avatar: The Last Airbender and
they finished a couple weeks ago. If you've ever watched ATLA in the past five years you know that even on the DVDs the visual quality is nowhere near as good as that show deserves, and this version is glorious. You can check the screenshot comparisons
here. I highly recommend using the torrent link and just downloading it episode by episode because the whole thing is 63 gb.
Also, if you haven't watched Avatar: The Last Airbender, oh my god please. This show is incredible. I always thought it looked like a dumb fake anime for children, and it kind of is for the first few episodes, but by the end it's actually the best show ever.