I think the main story is obvious, and I really don’t care what the sequel trilogy is about. It’s all garbage to me,
That is simple, because we know Alderaan is connected with the main characters.
Alderaan is mentioned throughout the first half of the film. If the audience doesn’t see it or know what happens to it, they will be pissed because of the emotional investment. Alderaan is where Luke and Obi-Wan are supposed to take R2-D2. Alderaan is where princess Leia’s father is, and we can further extrapolate that it is their home as well. It is because Luke and Obi-Wan need to get to Alderaan that they meet Han and Chewie. These established connections make Alderaan important to the movement of the plot. Yeah, it could’ve been any planet, really, but it’s not, it’s Alderaan. So when Alderaan is obliterated, the audience has an emotional reaction towards Leia, and towards Vader, Tarkin, and the Empire.
In TFA, we have no idea what planet the First Order blew up. There is no connection established with it to any of the main characters or even the minor characters. General Hux makes some speech reminiscent of the Nazis and they blow a planet and four other celestial bodies (presumably moons, but I suppose it could be the entire star system) with it. If it weren’t for the cut to the view planetside, we wouldn’t even have a clue to the significance it held (since due to the nature of the story, they couldn’t show Luke).
Instead of showing it in ANH, they had Obi-Wan feel it through the Force and describe it to the audience, leaving the terror to the imagination (which is always more effective than showing). Although we didn’t need a description to know the significance, as that was long established, it plants the seed in the imagination for its destruction. The fact that Obi-Wan is affected by it so much and he needs to sit down reveals how powerful the Force is and how sensitive Jedi are to it.
The destruction of the Republic planet doesn’t have have much of a narrative effect on the story, other than showing the power of the villains and that the First Order isn’t some fringe organization, nor does it have any emotional effect on the audience. It’s probably a Republic planet, judging from the Nazi Hux speech, but we have no idea why it’s so important. There’s a cut to the heroes and everyone in Maz’s cantina outside reacting to the destruction. They have no idea but know it isn’t good, and Han obviously has a bad feeling about it. This is bad storytelling! The only emotional content it has is it’s a ceremonial push of the reset button on Star Wars. Anyone hoping for a story that wasn’t a rehash of ANH had their hopes dashed at that moment.
Those cries of terror were from the Expanded Universe fans, and the terrible thing that has happened is that it’s no longer canon, and there is no hope of a proper sequel trilogy.