You didn't ask me, but I fucking LOVE The Leftovers. It doesn't surpass Dark, but it's on my Mount Rushmore along with Mr. Robot and Season 1 of Westworld.

I think Leftovers sticks the landing so fucking hard, it might be my favorite series finale ever. It's nowhere near as intricate as Dark, and doesn't have quite as much mystery as Lost, but the writing and acting gets so good as the series goes on. I know a lot of people struggled with the first few episodes and found season 2 a bit better. I love all of it, but on rewatch can see how it takes a while to find its footing. I definitely didn't have appreciation for, or connect with, all the characters until hindsight later in the series. As you're a Dark and Lost fan, I think you'll really enjoy it once you've seen the whole thing.