People may find it unusual, but my feelings from watching Dark and Attack on Titan are almost the same (I know the stories are vastly different from one another)
First seasons of both series were gripping from the very first episode. On one side, Dark gave us a fresh look at the age-old question, what can happen if time travel was possible; AOT with its stunning visuals and animation gave us a fresh outlook on the mythical story of David vs Goliath, humans vs Giants. Both seasons were like a roller coaster ride with unexpected endings, leaving us with more questions than answers.
With season 2 and 3 of both the series, we get to experience the layers of stories piling onto one another while happening concurrently. Viewers are given the opportunity to crack the enigmas, but as we keep peeling the layers to reach the center, we get the feeling of duality, it makes complete sense but none of it makes any sense.
By the time you reach near the center, you realize how human emotions are at the core of these storylines. You also realize how humans are bound by "fate" to repeat the same things and reproduce the same mistakes, which then has to be carried by the next generation or iteration. You feel that there's no escaping from this infinite cycle of tragedy and misery.
The Season finale of Dark gives viewers the ending we never expected but deserved nonetheless. We realize that a system in perfect equilibrium will always find its way to balance itself unless intervened by an external force. It answers all our questions (almost) but leaves us feeling more miserable than we were at the beginning.
The final season of AOT will be coming this year, and as I read the manga which is almost finished (just 3-4 chapters left to release) I realize how it will give us the ending no one ever expected but will make perfect sense in the end.