Brief review as an anime-only watcher, no spoilers:
As commander Erwin would put it, if you haven't watched this season yet - SUSUME! What are you waiting for?
While season 1 of Shingeki no Kyojin (aka Attack on Titan or AoT) was quite prone to melodrama, and was a little too punctuated by the MC trying to push his vocal cords to the limit while simultaneously trying to pop his eyes out, S2 feels like a much more mature show - with heavy elements of mystery and world-building taking the forefront. The action from the first season is still there, better than ever before. Wit Studio delivers on every front.
Story (9/10): There are no brakes on this crazy train. As mentioned before, this season gives a major emphasis on the mystery surrounding this bizarre Titan infested world. Where did they come from? Why do they kill humans? With this season, we finally get to step a little bit closer to the truth. The story is gripping, even depressing at times, almost reminiscent of the hopelessness in parts of A Song of Ice and Fire.
Art (10/10): Wit Studio did a fantastic job bringing the manga to life. Some CGI has been used, but it does not look out of place at all. Be prepared for some outstanding action sakuga as well as outright gorgeous-looking scenes.
Sound (9/10): The background music isn't outstanding, but nor is it bad - it's unassuming, and lets the plot take the forefront. The OP and ED are excellent, and the visuals are quite memorable - the ED especially, with a bizarre representation of the history of the AoT world.
Character (8/10): A lot of 'minor' characters from S1 get a lot of limelight here, to great effect - Eren isn't a very likable MC, and getting some time off from his antics allows the show to flourish.
Enjoyment (10/10): It's a wild ride from start to finish. There's mystery, horror, depression, death, crazy twists - even unintentional humour packed into this season.
Overall (9/10): Significantly better than the first season - to the point where it pulls the entire franchise up in my eyes. I'm eagerly looking forward to S3 to see more of the world of AoT being revealed. If you even mildly like season 1, watch this!