I assume by the way you've described your feeling of "void" you're not necessarily talking about an anime that will leave you depressed, but more that it just made such a huge impact on you that you feel that negative space effect of 

1.MAHOU SHOUJO MADOKA MAGICA

What does it take for a series to become a masterpiece? Take a look at Mahou Shoujo Madoka Magica, and you might find the answer to that question.

2. KATANAGATARI

Katanagatari is interesting because it's one of the better anime in recent time (that I have seen), one of the best anime from 2010 (that I have seen) and arguably the best work of NisiOisiN (that I have seen, even though this only includes two titles).

Now, Katanagatari is great, it's absolutely wonderful, but depending on your ability to immerse yourself in a story so much that you forget time.

3. Gurren Lagann

Gurren Lagann was breathtaking. An endlessly thrilling ride from the most humble beginnings to the most fantastic of ends. Absolutely inspiring and a must-watch. There are so many memorable moments in this series, and lines and ideas that it imprints into your very soul.

4. Akame ga Kill

To kill or not to kill, that is the question. In the world of Akame ga Kill, it’s more than just about killing as survival fits to those who wish to live for something to fight for.

5. Plastic Memories

When I first started watching Plastic Memories back in April I was immediately very impressed by it because the first episode was simply amazing. It forecasted an original anime with beautiful artwork, an ambient atmosphere, likeable characters and a lot of tragic drama.