If you are looking for the good things I have to say about TLJ, you can start at:
https://chrismlegg.com/2018/01/16/star-wars-the-last-jedi-review/
But now the problems – these are going to come fast and furious and will feel like they are being machine gunned.  I apologize for the cheap writing here – I might should have done it all in bullet form, but I want to get to the deeper stuff:
“Mulling over” power
One sign of a great movie, in my opinion, is its “mull over” strength. As I sit and ponder a movie, it should get better in my mind. I should start putting pieces together and having new revelations, etc.
This movie has been the opposite. For someone who likes to consider and talk about movies, this is an important feature for me.
SWTLJ scores dismally on this category. From little things:
Bombs “dropping” in space?
Ships “falling” backwards when they run out of fuel in space (I know SW has never taken space physics seriously, but this was laughable).
A giant fishing spear
Tracking through hyper space
Magic missiles that ignore shields
Jedi nuns
Newly created jedi powers (more on that later)
Light speed as a weapon, new “bombers”,
We have to get to the planet to send out a signal, except that of course, we can somehow communicate with Maz in the middle of a gunfight.
Wrecking your salt-speeder is sometimes pretty deadly – but sometimes it saves your life when someone smashes into you.
Tracking through hyper space?
Projection Luke carries dice that somehow wait to vanish later.
Did I mention, tracking through hyper space?
And dozens of much worse examples that, as I sit and think about it, I go “wait… but what about…” and conversations with others just becomes a snowball of all kinds of problems.
If you want a play-by-play of the dozens of gaps and holes and things we have to ignore to stay in the movie, check out this review series.
This, as much as anything else, reminds me of Ep1-3.  The more I mull it over, the worse it gets.  I cannot tell you how much I hate this in a movie.
Consider Rogue One as an opposite example of this. I was not really blown away the first times I saw it (though I enjoyed it), but the more I think about it, the more I like it.  Ep 5 is certainly that way!  As a kid, the first time I saw it, I was horrified, but as I have analyzed it, it grows in excellence.  The more I talk about it, the better it gets.
Great movies have this.  Check out “Searching for Bobby Fisher” as one of the greatest examples of this of all time.
Plot issues
Circular, meaningless (and in some cases, boring) subplots – This is combined with circular, (and so far as I can tell) meaningless characters (which will come up next on this list). For example, if Finn and Rose had just tried to sneak straight into the FO armada and been captured, the plot result would have been identical to what happened.
Granted, we wouldn’t have gotten to see how bad rich people are, but I guess I could have survived without that message, too. Think it was about teaching Poe, yet again, a lesson about his pride? Then have it be his idea and founded in his certainty that he could make it so they could get in.
Another circular plot?  The Dark side of the island. We spend a lot of time learning and gaining nothing. Was that the point? What kind of point is that, if so?
In Ep 5, Luke sees himself in the Vader mask – giving him possible insight into Vader’s connection to him and his potential to join the DS. Rey sees mirrored of mirrored images of herself – indicating what? That there is nothing more to her than what she sees?
Running to a planet to call for help to have none come is not much of a plot device. Luke’s whole stalling of the FO just so they can escape out of a back door (“back door, good idea.”) changed nothing. Getting to the planet was a circular plot regardless. Now they are back in a ship going into hyperspace where the FO can track them and did they get more fuel? Does that matter?
And then there are the unfinished plot issues – Snoke ends up having no role in the plot (unless Abrams gives him one in Ep 9). Where did Luke’s light saber come from? Is that the truth about Rey’s parents?  Was this movie more offensive to the plots, characters and universe of 4-6 or of 7?
And, of course, the fact the Ep 8 essentially makes 4-6 a meaningless plot line and even makes ep 7 a meaningless plot.
New Plot Devices
New devices in an existing universe is a really bad idea. It creates all kinds of reverse re-interpretation of that universe.   It begs all kinds of questions:
Listen, only a few people have the genius to create a universe with rules and then stick to them. Tolkien did. Sanderson is the master. With all of her genius, Rowling struggled greatly. Lucas lacks that genius.
I know that the abilities of Jedi have always been based on the plot and the more input Lucas has had, the worse this has gotten. (Higher ground? Really?… “I sense a plot to destroy the Jedi” – the cringe factor makes it hard to even type that stuff.) Even in the originals – Luke can choke Gamorrean Guards, but not the Rancor… or Jabba? Jedi Mind control is completely plot dependent…   but Ep 8 takes us to whole new levels of new plot devices.
This movie should be used in training classes for many years as one of the worst examples of this ever.
Jedi can force project themselves over light years?
Jedi can kill themselves by overusing the force?
Jedi can fly in space without a ship?
There is stormtrooper armor that reflects blasters?
The force works when you are unconscious?
Force users can see each other from light years away and talk?
Light speed can be used as a weapon of enough power to destroy an armada?
The force automatically raises up LS force users to match DS force users and vice
versa – and one of them training increases the other one’s power?
Well, then…
Why did Jedi use comlinks?
Why isn’t all stormtrooper armor like that (don’t say cost – these people have the $$ to convert planets into guns).
Why didn’t Yoda project himself to cloud city to warn Han?
Why wasn’t Yoda training Luke the whole time from Dagobah?
Who was Vader’s LS yin/yang? Who was Luke’s? Obi Wan’s? Are they like Harry Potter and Voldemort – what happens if one dies but the other doesn’t?
Why didn’t we launch “light speed” weapons at the death star, or at the Imperial Armada? Why didn’t the FO do that to finish off the resistance?
And on and on… don’t worry, there is plenty more…