People are always so shocked when I say this is my favorite marvel movie... but truly, it is! Heres why;
Previously marvel movies have been all about good guys vs bad guys. This movie is about avenger vs avenger. Allies form, action occurs, and relationships begin to crumble. Previously Captain America and Iron man have disagreed on various small things, but in this movie you truly get to see a different side of each character. The movie forces you to pick sides, you're either team Iron man or team Cap, and that really just changed the whole dynamic of the movie to something fresh and interesting.
The characters! Often times I have a hard time watching some of the Marvel movies that are about characters I don't find very interesting, but this movie truly has everyones favorite in one scene or another. You can see new relationships form, unlikely ones such as Wanda and Vision, and it makes everything come together really nicely. Personally, my favorite is and always be black widow, and I loved seeing the way she changed throughout this movie, and the chemistry between her and cap is UNDENIABLE. Whether you're a die-hard Iron man fan, spider man fan, Wanda fan, ect, you can find your favorite avenger in this movie somewhere, and you will love the role they play guaranteed.
Some people say this is boring.. and to that I say I think you've missed the point of all of the marvel movies thus-far. I've read through some of these reviews and someone said it was "extremely boring" and to that I say, do you not care about the characters then? The entire point of this move is expanding on characters and their dynamics with others. Yes, the world isn't at stake in this movie, but its an internal war between the life saving forces of the entire universe. If you don't find that entertaining.. well you might need to check out another franchise.
In total, this movie is brilliant. LOVED IT! I re-watch it multiple times a year, and I love it every time!