I saw it and thought it was really good. The premise was a bit stupid (sending two regular troops to send a critical message), but the cinematography and depiction of WWI was very good. I am surprised you found it boring since most of the movie was suspenseful action.
On the other hand, I don't recall liking Dunkirk at all, but maybe that's because I didn't watch it in a movie theater. 1917 is definitely a movie you have to watch in one sitting (and possibly in a movie theater) to get the full effect of.