I am 45 hours into this game and I feel like I've played enough to determine this is fantastic. Decent storyline, with a brilliant range of choices that determine the path you take. The gameplay is where this really shines. The parkour moves are incredible and the best I've seen in a game. On top of that, the melee combat is satisfying and intense. There's a strong, detailed RPG system here, that allows you to progress and manage your gear that will determine your style of play. The world itself, feels dense and full of content. There's nothing quite like running across rooftops, then seamlessly diving into windows. It's this level of density to the world map that makes exploration so exciting.
The story is strong enough to keep you going through out the campaign. Voice acting and writing can differ wildly. On one hand, the main characters are pretty strong actors, with only a few iffy lines here and there. But some side characters can sound like charactatures of themselves. However, this is never an issue and they serve as a means to an end, in terms of side quests.
This game has it's flaws but being an enjoyable open world experience, isn't one of them