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.
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.
Base Breaker: 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 auhorial style while disapproving of the plot. No other grounds seem to exist.
Harry's confession about the merger with his future self in the Chamber of Secrets.
The Mean Brit: Mr. Granger sometimes skirts into this territory, but he's overall well-meaning.
Unfortunate Implications: The fact Harry is actively wiping out any perceived flaws from his friends to make them better people. He intervenes to stop Ron's jealousy, Hermione's bossiness, and Ginny's shyness and congratulates himself on the fact they're turning out to be different people. While you can also see Harry's point of view; he's trying to help them become prepared for the difficult road ahead, it doesn't quite feel right that he's willing to change his friends to be better than the original friends that he knew. On the plus side, Harry is acutely aware of the Unfortunate Implications in-universe and is actively questioning his own motives.
He is trying to make sure they reach their full potential earlier and avoid all the messes that put their friendship in danger, but, yes, he knows that this is not quite right.
Harry encouraging a, what he calls, 'healthy distrust for authority'. Though given that this is the Wizarding World we're talking about...