I've played every game in the franchise, including the lets say, less than stellar ones, and honestly Shadows is a breath of fresh air. The combat overhaul is very well done and the new stealth in absolutely insane. It takes many elements from other games such as Splinter Cell and integrates them into the mechanics quite nicely. It feels like Assassin's Creed, which has been a problem with the last couple entries.
If you're a fan of the AC series, and especially of the older games, like Brotherhood, then you'll absolutely love Shadows.