These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Clear Sky. Is he a sympathetic antagonist with a believable Freudian Excuse, or is he just a hypocritical jerk who deserves to die?
Storm is either seen as an interesting and fun she-cat or a boring excuse to create romance drama.
Wind Runner became one due to her actions in Thunder Rising and The First Battle, in which she is shown to be a warmonger and fuels the rivalry between the Moor and Forest groups. Some people think that she's sympathetic and well written, while others hate her for these actions and want her to go down.
Jagged Peak, mainly due to his treatment of a newly returned Thunder in The First Battle. Was this behaviour understandable due to his experiences with Clear Sky? Or is he just a jerk?
The time period of the series. Some fans like the idea of a prequel and think The Last Hope wrapped things up well, while other fans want to know what happens after the battle. However, it appears to be dying down with the positive reception of The Sun Trail.
The treatment of she-cats in The Sun Trail. Some fans think that the she-cats got shafted in terms of character development and the book is full of misogyny. Other fans don't agree and think the complainers are just being obsessive.
Thunder Rising is the most divisive book in the series, so far. Is it good, but not as good as The Sun Trail? Is it an Even Better Sequel? Is it a terrible waste of all of The Sun Trail's potential? It depends on who you ask.
Come for the deaths, stay for the character development.
Come for Gray Wing, stay for Tall Shadow (or Jagged Peak).
Continuity Lockout: After the amount generated by Power of Three and Omen of the Stars, this arc for the most part avoids it. Someone with no knowledge of the rest of the Warrior Cats series could pick up a copy of The Sun Trail and completely understand it. However, it still exists in small qualities. If this is a reader's first Warriors book, the beginning scenes featuring the Tribe will lose some of their impact, and the last chapter's rather awe-inspiring reveal about Thunder will fall so flat that new readers won't even realize that it's a twist.
Some fans admitted to reading The Sun Trail solely because they wanted to see River. Subverted in that he's the only Clan founder that didn't show up until the second book, Thunder Rising. Then fans could enjoy his presence.
Quite a few fans only read the book because of the beginning scenes with the Tribe.
"Shaded Moss, actually", Tall Shadow's legendary retort when Moon Shadow sarcastically asks who died and made her leader.
Snake from The First Battle being a Clear Sky fanboy has spread to tumblr. Some◊ examples◊ (mandatory bad art).
One-Scene Wonder: Nightheart showed up, spoke two lines to Gray Wing and Clear Sky, then swam off. A fanbase was born.
Replacement Scrappy: Subverted with Holly. You would think she would be this, being Jagged Peak's actual mate, instead of Rainswept Flower, who died in The First Battle, but the fandom has responded quite well to her prickly personality.
Sacred Cow: The Sun Trail has become one for fans. Bash it at your own risk.
The Scrappy: In The Sun Trail, not a lot of people liked Moon Shadow, because he was a complete idiot and a deadbeat dad.
Ship-to-Ship Combat: The introduction of Star Flower has been taken as a huge blow by the Thunder/Acorn Fur shippers, and a lot of them are getting angry. And what the Thunder/Acorn Fur shippers are going through is nothing compared to what Thunder/Lightning Tail shippers are feeling.
Win Back the Crowd: After the lukewarm reception of The Last Hope and Yellowfang's Secret, The Sun Trail's faster pace and fresh ideas made a lot of fans declare it one of the greatest books in the series. And if it didn't win the crowd back, then The First Battle definitely did.