YMMV / Harry Potter and the Nightmares of Futures Past
Alternative Character Interpretation: Harry, for obvious reasons. He comes across as having more of an American action hero feel to him; he keeps a gun because it might come in useful, he drawls, he's quick to throw witty and sarcastic remarks at authority figures, and he draws a lot of inspiration from American military procedures. It does make sense as older!Harry did spend a lot of time with the Americans following the deaths of his friends but it can be jarring when comparing him to the very British school boy he was the first time around.
Mr. Granger gets the biggest change of anyone, as he is turned from someone who is implied to be a bit timid from canon sources into a thoroughly stubborn, opinionated, highly demanding overprotective father who reacts negatively to the idea of boys interested in his daughter and was actually prepared to pull Hermione out of Hogwarts with no thoughts as to how she felt about it. He even blamed Harry for the racism present in the magical world. This is especially jarring considering Mr. Granger is supposed to be a dentist, yet he's the most hard-assed dentist one could ever hope to meet.
Charlie Weasley also apparently gets a change from "genial older brother" to "insanely overprotective brother" who feels the need to make death threats against Harry.
This happens after Charlie learns that Harry is, in mind, older than him, so perhaps he was going the "insanely overprotective brother" because he did not want his sister to "fall prey" to someone that might be manipulating her.
Broken Base: For the same reasons as Team 8. It's partly due to both fics' overbearing popularity, but a number of readers simply dislike the way in which many events and characters are depicted overall (and this isn't just limited to Shipping). You're either going to love this fic, hate it, or respect the authorial style while disapproving of the plot. No other grounds seem to exist.
Hype Backlash: The level of attention and praise it gets in forums as a Fanfic Mastership can colour the expectation of future readers to impossible levels.
Ron the Death Eater: Does this to both the Dursleys and Snape. Tropes Are Not Bad; the author explicitly wanted to show the natural effects of these characters' abusiveness. Dumbledore, though, becomes a Well-Intentioned Extremist who believes in the ends justifying the means. It does turn out to be refreshing, as he is more of an Anti-Villain than the usual "For the Greater Good" characterization that fans are so fond of using.
And Snape, at least, can also be partially explained by the fact that the fic started before Book 7 came out and revealed his true backstory.
Shipping: The story follows the canon ships of Harry/Ginny and Ron/Hermione, but it also tosses in a new one: Neville/Luna. (As if you didn't see that coming.)
Harry's confession about the merger with his future self in the Chamber of Secrets.
Mixed with Crowning Moment of Heartwarming; Harry realizes that he had spent much of his first year pestering Hagrid about who Nicolas Flammel was and was simply taking advantage of their meetings for that. Thankfully, he knows about the Stone now and decides to simply enjoy his visit with Hagrid alongside Ron and Neville.
Neville hearing Hagrid talk about his parents while they were at school. After not knowing much beyond what his grandmother told him and what everyone expects of him because of his parents, it must have been a shocking change in pace for Neville to simply hear a story where he isn't compared to his parents.
Luna's calm reaction over the revelation that Neville's grandmother is keeping Neville away from the others during the summer because of her. She blames herself and offers to stop coming if it meant Neville could be with the others.
Melissa Bulstrode's death and Slytherin House bullying her sister afterwards.
Malfoy and his "friends" suggesting that Hermione does all of the homework for Harry, Ron, and Neville, and also "spreading her legs". Hermione is reduced to tears.