I've spent a lot of time thinking about why I loved episodes 4-6 so much, and why it's so hard to make a new Star Wars movie that pleases me, and I think I've figured out the answer. I was born in the 70s and was a kid at exactly the time when the original trilogy was huge. Return of the Jedi was the first movie I ever saw in a theater. I watched the cartoons. I had all the action figures.
There's a phenomenon which happens on farm yards when baby chicks hatch called 'imprinting' where the chicks imprint on whatever creature they see first as being their mother. If the farmer's dog walks past, then they'll imprint on it (this is slightly hyperbolic, but you get the point). The way I figure it, Star Wars imprinted upon my young mind, and my love for the first trilogy is ingrained deep inside me. This makes in nearly impossible for anyone to ever create a movie that competes. Poor George Lucas didn't realize this when he made Episodes 1-3: You simply can't live up to an entire generation's nostalgia.
J.J. Abrams saw what happened to Lucas with E1-3 and realized the minefield that he was walking into, so he just played it safe and to avoid the nostalgia trap, he simply made E7 a direct plagiarism of E4 (if you haven't seen the parallels, just go to YouTube and type in "star wars episode 7 episode 4 rip off").
I thought Rogue One was an excellent movie, nearly perfect, until they dropped the ball literally on the goal line at the end of the movie and placed Princess Leia at the battle of Scariff, creating a huge consistency problem with E4, despite the fact that the whole point of R1 was to set up and explain E4. Sigh.
E7 and E8 certainly aren't anywhere close to even R1, and I don't need to cite nostalgia to rip them apart. There are dozens of major flaws with them, and many have already been pointed out above, so I'll just focus on my major complaint, which is that Kylo Ren is a wuss. He's not a super villain that commands respect, but instead is the most emotionally vulnerable and insecure bad guy in cinema history. It's like they took Ross from Friends at his whiniest and just draped him in a black cape. What the hell?!? Darth Vader was cool. He would force choke and murder subordinates that displeased him without ever even raising his voice. No whining or self-doubt. Now that's a proper villain worthy of fear and respect! Kylo is the opposite of that, and he's simply not worthy to be the villain in a Star Wars movie. This ruins the whole new trilogy, and there isn't really anything that can be done to offset this massive flaw.
And then in E8 they took Luke and turned him into a self-doubting whiner as well!!! What happened to the awesome dude who stood on the plank above the Sarlacc pit on Tatooine and told Jabba, "This is your last chance..."? You know what's even worse than not living up to my childhood nostalgia? Going and desecrating it by ruining my hero! What were they thinking?!?