The story was good! The side missions weren't worth it. The open world was confusing and disorienting.
Besides all that, the story missions are very good and worth playing, mainly because they TAKE PLACE INSIDE the buildings and not on the open world. The fighting is good and you upgrade quickly acquiring lots of gadgets and new moves, you hardly ever use the new moves but ok... The BEST thing is the stealth action, there are a lot of places to hide and takeout your enemies, it's not easy taking out all the enemies without noticing you but if you plan your attack beforehand you can actually make it.
Play the side missions and/or the dlcs before finishing the main story, eitherwise you will get bored playing them afterwards...