I'm satisfied Mikasa overcame her depression, at least to a degree, so quickly. She was always quite a dark character (after her tragedy, anyway), so I imagine she wouldn't have any weapons such as cheerfulness to combat dead-end emotions. Although being obsessed about Eren is an integral part of her character, so I'd say dropping that to go on would be bad.

But yeah, I was also looking forward to seeing the abnormal titan animated.