First of all those awful one-liners throughout the whole film.
While I do like them in many films and most of the time they add a certain flair, especially in films that don't take themselves to seriously (e.g. The Expendables or basically any Bruce Willis film), in JB
they feel totally forced on every occasion.
Lets put it like this: I laughed on the first one, then on the second, but when they threw the third, fourth, fifth and sixth in my face ins less than what felt like 3 minutes I was like: "Seriously? Didn't they have enough money to write proper dialogues?"
This brings me directly to my next point:
The film can't decide IMO what it wants to be. On the one hand it proclaims to be all grown up (e.g. the "Oh Mr. Bond we don't do exploding pens anymore" stuff), then on the other hand they do completely retarded action scenes (my favourite example here is the helicopter crash resulting from the gas explosion in the manor at the end of the film. While the gas explosion seemed somewhat "realistic" the explosion from the crash is completely overdone, ripping the whole house to shreds and being bigger than one from a bomb.
Just as a second example: the bad guy dying for roughly one or to minutes after having been thrown a big ass knife into his back which pirced him all the way up to the hilt. And I don't mean the "lying on the ground and bleeding out " kind of dying but the "I'm gonna take another step towards you grunting, oh and another one, oh and another one, oh and another one, oh and ..." kind of dying.
Third point:
Moneypenny is suddenly black. While I like the actress and I think she does a very good job at playing her role, I simply can't stand the point that Eve Moneypenny is suddenly a black girl. (This has nothing to do with racism ofc, I thought the same way when Lavender Brown in Harry Potter was suddenly white)
Fourth point
The bad computer animations. Those giant lizzards in the casino, or the guy falling out of that skyscrapper just looked like they were done by a college computer art design freshman. They looked like they were from a low-budget movie.
And what I can think of lastly atm are the gaps in explanation of the plot.
My favourite examples: who was that guy shot in Shanghai by the henchman with the harddrive, what did he have to do with the rogue agent? Why is there such a coincidence that this was a job done for the rogue agent?
How did they infiltrate MI6, okay they used the hacking stuff, but then how did they get the gas in the vents to blow M's bureau to smithereens? Was everyone asleep in there?
James Bond was declared dead, all this stuff was sold, his bank accounts presumably frozen, how the hell did he suddenly get back to England from whatever part of the world he took his timeout in?
There are other examples, but I'm not in the mood to make a full list atm.