Some stories, you look at the first few pages and know EXACTLY what this is going to be: a lighthearted action flick. A detective omnibus that's also a witty commentary on the sucky sides of life. An honest, unglamorous look at teenage romance. The Pianist (2002 movie) is one of my favorite movies and is a good example of this. It starts out like a somber wartime civilian drama, and it stays that way for the entire length of the movie. It certainly develops and grows, but does not change its tone.
But there's another school of storytelling, stories that take longer to figure out. Keen readers may see it right off the bat, but in general, people will need time to really know what your story is trying to do. The Last of Us is one example I can think of; its intro is laden with drama, but you assume it's a horror story... because it's a horror game with horror settings... but in the end it's really a character drama more than anything IMO. The further you get in the game, the more you realize the story is far more depressing than it is scary.
Of course, then there are stories that are in-between.
I'm not here to argue which one is superior/ more difficult/ etc. That would be pointless! But which approach do YOU gravitate toward, as a reader and as a creator?
Me, I enjoy both (+the in-betweens) pretty much equally as a reader. But as a creator, I find pretty much all of my longer stories shift tones. It's not uncommon for people to describe my stories as genre X at the beginning, then as genre Y later. While I'm still learning how to handle the shift better, the fact that the shift is there isn't a bad thing in and of itself.
(PS. Tapastic, STOP trying to tell me this topic is similar to "looking for an artist to work with." What are the similarities!?)