Before seeing Deadpool, I thought it was just a regular superhero movie.  I have nothing against those movies, and I often enjoy them, but even when they're well done, they don't really stand out.  Yes, the Avengers had good action and good jokes, and I'm glad I saw the movies, but it's not a favorite or anything.  Action movies typically aren't designed to make you think, and they often don't have that interesting of an artistic style (with notable exceptions like Kill Bill).  However, with Deadpool, I saw a PBS Idea Channel video on Deadpool (the PBS Idea Channel distills dense philosophical concepts and relates them to popular culture) which convinced me that Deadpool had a very interesting relationship to the fourth wall and made me want to see the movie.  I wasn't disappointed.

The action was good, and the crass jokes were funny, but it was all of the self-aware humor that did it for me.  The movie manages to employ those to great effect from the start (the opening credits that Deadpool even references in his own Honest Trailer) to the end, with plenty of references inbetween.