I really enjoyed Unity. The parkour is easily the best in the entire series plus it added a fun little coop style of gameplay. The story... It isn't the best story but I loved it. There's more of a romance subplot than any other game.
But I do suggest that if you play the game that you read the book Assassin's Creed Unity afterwards as it shows us what Elise ( The love interest) was up to during the events of the game.