The Stalking Zuko Series is an interesting concept for a fic, being told as Katara writing a diary about Zuko that chronicles her progressing from reluctantly accepting him into the Gaang, to befriending him, to falling in love with him, as well as her perspective on all the events that happen during this process.
Katara's narration is effectively done. It fits the mood of the story, being funny in lighthearted scenes, and helping us feel for her in more serious parts. It also nicely chronicles her changing perception of Zuko.
Most of the characters are nicely fleshed out and portrayed realistically, with their personalities expanded on. Some, such as Suki, get expanded on and become somewhat more interesting than they were in canon. Others have running plots dealt with, as Toph has to deal with her parents, and those are, for the most part, dealt with quite effectively and compellingly.
However, Aang seems to get the short end of the stick, for the most part. He's frequently shown slacking off in training, and is never allowed to make a good point in debates. The part dealing with him sparing Ozai reads like an Author Tract
against the ending of the series, with the characters forgetting that he defeated Ozai and saved the world without going against his principles. The author claims to have nothing against Aang, but one would think that Aang would be smarter and more effective than he is in this story.
The fic also reads like a Fix Fic
at times, with the author changing various parts of canon according to her own preferences, or adding things that the characters should have done. Granted, this happens quite often in fan fiction, but it's fairly noticeable here.
The plot allows for a variety of situations involving Zuko, although it moves quite slowly at times, with many chapters passing between certain points in canon. There are quite a few scenes, but if you get into reading this, be prepared for a long haul.
All in all, this fic is quite well done in many ways, but it also has quite a few noticeable flaws, and you should read this only if you can deal with alterations to canon and various characters getting shortchanged.