Gantz, I never heard of it but if its anything like AOT, I might want to read it. As for the AOT deaths being important, some of them are more important than others of course. I think *SPOILER ALERT*, Spoiler
that Hannes death was really important but that might just be as it saddened me.
One thing I will say about Hajime Isayama is that he has great character development and he might have created one of the bravest characters manga have ever seen, Eren Jaeger. His determination to wipe out the titans is second to none, but I do have a prediction for the ending of the story.
Prediction: Eren Jaeger, now surrounded by titans attempting to protect the now breached Wall Sina alongside The Military Police Brigade and the remaining forces of The Survey Corps, fights in an advanced state of Rage Mode that allows more strength than before also increasing his speed. Fighting alongside Mikasa, Levi, Armin, and Grisha Jaeger also a Titan Shifter with a 25m class. After a futile attempt at saving mankind, Eren becomes a titan once more but has achieved the height of 70m! Once receiving such an height, he then uses his titan in order to create a wall, along with a controlled army of his titans creating a new wall surrounding Wall Sina.
After the creation of the 70m wall, the humans could live in peace once again, but they will ready themselves for the next breach and this time reclaim humanity. Following the sacrifice of Eren, the new wall was named Wall Kalura after Eren and Mikasa's mother. Mikasa saddened at the loss of her brother, becomes the new Trainer of a Scouting Legion Trainees Squad. Armin becomes a Scientist in hopes of discovering all of the titans information in order to get an upper hand the next time they encounter one. After years of preparation, Mikasa and her trainees numbering in around 500, set out to reclaim the world lost with Mikasa wearing the "Wings of Freedom" on a cape.[/b][/font]
Other Prediction: Nearly everyone important dies and the titans succeed at wiping out the human race.