It wasn't notable enough to be truly horrible, it was just incredibly lame. The story was not half bad, but the execution was just horrendous.
To start with, it moved too fast for us to emotionally get involved with what was going on. It was just paced badly. The dialog was so utterly un-sparkling, just flat and boring.
And the characters, cripes almightly, they made Deadpool boring. How the hell do you make Deadpool boring? He wasn't even funny. He wasn't crazy. He was just an annoying guy with a couple of swords he did not even know how to use properly.
Gambit was boring. And since when did he have telekenisis to make the cards just float and fly around, or super strength to leap hundreds of feet into the air? And what the heck was up with all the stupid helicopter moves? I mean, we know they are mutants, but they still exist within the realm of physics. A round bo staff is not a helicopter blade, you cannot fly by twirling super-duper fast. Which Gambit wouldn't be able to do anyway. Nor Deadpool, especially when using it as a replacement for real fight choreography.
And this film stands as proof that wire work should only be used by fight coordinators who know WTH they are doing, and know better than to use it in every. single. shot. as a replacement for real fight choreography.
Three of the most physical fighters in Marvel comics (Logan, Creed, and Wilson), and some of the worst fight choreography I have ever seen in recent film memory. It was as if the stunt coordinator just shrugged his shoulders and left it all up to the special effects guys.
And then you had the break out, with all these mutants who did nothing. Even mutants who had been shown in their cells to have powers (nice to see a Quicksilver nod), did f-all when they got out. Only Emma-really-lame-for-this-film-Frost and Cyclops did something.
And since when was Logan so pretty? And the stupid, "The bullet will take his memory away." Don't you think Xavier and the X-Men would have noticed the big freaking bullet holes in his adamantium skull when they X-rayed him in X1? I felt sorry for Liev Schrieber man, he actually brought in a good Sabretooth considering the script. He made one of Marvel's more simple super villains feel real. But he could not save the film from it's own epic lameness.
Seriously, this was "Daredevil" level of suck. Decent story, good actors, absolutely horrible execution.