First and foremost, the movie was fun.
They took the best parts of Singer's two films and the best parts of First Class and mashed them up into a really enjoyable whole. The action scenes were well choreographed, the stakes seemed high, the dramatic and comedic moments both landed, the nice touches and references to the comics were great.
I was expecting to hate Quicksilver, but I had a massive grin on my face for most of the time he was on screen. The nod to Magneto being his father, without outright stating it was great.
My favourite scene was Trask being grilled by the congressional committee at the beginning of the film. The appearances of Chris Claremont and Len Wein were fantastic.