I had X-Men everything as a teenager in the 80's and was thrilled when the the films came along. While I enjoyed them I don't find myself going back and rewatching them. The MCU films I stop on when I'm channel surfing and even pop in the dvd's occasionally.
To me, the MCU is like a close version of comics brought to life onscreen.
The XCU is like a series of "What If" comics brought to life onscreen. I might enjoy them more if I wasn't so familiar with the source material.
Performance, casting, and characterization is good but there was just something missing for me.
TFA set things up for the Avengers, and TWS. Red Skull should have had more action and his constant "curse you Captain America" got old quickly. The supporting cast was, without exception, excellent and under appreciated. Toby Jones was great, Atwell was stunning and convincing, Tommy Lee Jones played Tommy Lee Jones better than anyone much like Samuel L Jackson plays SLJ better than anyone. Evans and Stan did a great job making their friendship/brotherhood believable and poignant. The scene where Steve "dies" and Peggy tries to hold it together has more dramatic weight than anything I've seen in the comic book movie list so far. For me this is the deciding factor in that the MCU has managed to make me care about the characters in a way Singer/Fox/Sony/DC have yet to achieve.
Guardians of the Galaxy has proven that any character is viable, its the execution that determines success.