It's easier to name many movies I didn't like, but the worst is more than I can process. As for Deadpool, I've seen worse, but for me it was the low point in the pre-Disney Marvel Universe, and I am a big fan of the Marvel Universe, which has impressed me more than any other Hollywood phenomenon in my lifetime. Although, since Stan Lee died, and Marvel sold out to Disney, Marvel appears to be sinking fast. Disney makes good movies, but they don't seem to be able to duplicate the writing or creativity of Marvel.
Deadpool went over very well with critics and audiences, and I think Ryan Reynolds is one of the most talented people in Hollywood right now. I thought the movie was stupid. I didn't even bother to see the second one.