My primary problems with it were (note it is all subjective):
1) Resetting character development
It seems as if a lot of main characters had their development reset, or have spontaneous personality changes:
- Rey:
TFA: Kylo murders her father figure and wounds her best friend
TLJ: All is forgiven after a few minutes chatting - Finn:
TFA: Character arc about overcoming his cowardice, and falling in love with Rey.
TLJ: Goes back to being a coward, gets new love interest - Hux:
TFA: Genuinely intimidating, seems to be the one of the few non force-sensitives that is actually taken seriously by the supreme leader (he seems to be treated on par with Kylo). Implied to be in charge of/having developed their program of raising storm troopers from birth.
TLJ: Comic relief - Snoke
TFA: Seems competent, intimidating
TLJ: Jokes around
Simple enough, it personally irritates me that we will not find out where the heck he came from, what he was doing during the previous trilogies, why he doesn't consider himself a Sith, or why the Imperial Remnant decided he should be in charge.
3) "Spark of the Resistance"
This film seems very fixated on the theme that Leia/Rey/Poe and the 20 or so other survivors on the Millennium Falcon are the "ember" that will re-start the flame of the resistance. It is something that the characters repeat over and over again, and they emphasize how vital it is that they escape.
Problem: They're 20 guys in a space U-haul truck! They have no resources! The best they could offer a rebellion is: a) Information about military stockpiles: uncertain how useful this will be, stuff from the original trilogy would be out-of-date, and in TFA the rebellion was more a black ops being funded and run by the New Republic, seems questionable they'd be creating any sizeable caches of equipment b) An experienced commander: admittedly useful, but hardly unique c) Name-power: Questionable, they'd probably be just as effective as martyrs d) Rey: Useful as a trained(ish) force sensitive, but hardly indispensable (just look at the status of the rebellion in Ep IV before Luke shows up)
I guess it just really irks me that they seem to think that they are the only people who would or could run a rebellion. Even if they all kick the bucket, it seems doubtful that no-one will ever think of opposing the tyrannical and oppressive First Order. Makes 'em look like a bunch or raving egomaniacs to keep implying otherwise.
4) Spontaneous love interest
I'm fine with Rose's character. I do not like the fact she spontaneously falls in love with Finn at the end (again, just my opinion that it was rather out of left-field).
5) General logical problems
- The collapsing ship that knows to drop the floor out from under Phasma, but not out from under the 2-tonne walker running about with the protagonists onboard
- I feel that hyper-drive ramming breaks the logic of all previous films
- Characters making stupid decisions in general (i.e. Hux not jumping ahead and destroying the fleet, the fleet not splitting up or at least getting ships to jump before they enter firing range, Holdo not reassuring her crew, etc...)
- The entire Republic fleet was apparently in the capital system, at the same time. That's my best guess as to what happened to them.