Funny... I loved the score, got even a complete edition and I am still listening to it... especially the main theme (titled 'Logan through time' on the OST).
Different people, different tastes... it seems.
I liked the cameos (too bad they left Storm out in that African village), especially Xavier's cameo at the end. Made a superb climax for me, and was a very pleasent surprise.
Which action sequences were average, exactly? I thought they were all executed fairly good, especially the Bike sequence and the final fight were just awesome scenes.
As for Deadpool. I had no idea he had a different backstory. But honestly, everything came together in the end, so in the context of the movie itself, this story worked (at least for me)