You will be fine without playing the others.
As far as the gameplay, I like it and I really disliked the other AC games. I mean the combat is still pretty much the same but the Pirate aspect is cool. You get to sail your own ship around and go where you want, do what you want.
I might pick it up then. I just got done with two long RPG games, so I don't really want FFXHD or Bravely Default at the moment. Titanfall I really don't want that much, so if I can enjoy AC4 having not liked the others (and have no clue about the story of the others) I'll probably pick that up because the whole pirate/ship thing seems really interesting.