What makes the Code Geass ending so acclaimed?

The Zero Requiem finale works on multiple levels simultaneously: as political strategy (it actually achieves world peace), as character resolution (Lelouch completes his arc by choosing death over survival), as emotional gut-punch (Nunnally finally understands after it's too late), and as thematic statement (the only way to achieve good ends through evil means is to sacrifice yourself on the altar of your own evil). It rewards everything you've watched and recontextualizes it.

How does the ending handle the supporting cast?

Carefully. Suzaku carries the weight of being Zero forever — an enormous sacrifice of identity. Nunnally gets the world Lelouch built but loses the brother she didn't know she had until the last moment. C.C. is left alone again. Each character's ending is earned by their arc.

What does the final scene mean?

Lelouch, bleeding out in Suzaku's arms in the Zero costume, reaches for Nunnally's hand. She takes it, sees his memories, and understands — everything. His love for her, his plan, what he sacrificed. She cries "Lelouch!" rather than "Zero." The series ends ambiguously on the possible-cart-driver image, suggesting survival while leaving room for interpretation.

How does it compare to other major anime endings?

It's one of the few finales that achieves every character's arc, resolves every plot thread, and delivers an emotionally overwhelming moment that grows in power on rewatch. Death Note's ending is satisfying but emptying. Gurren Lagann's is cathartic. Code Geass's is uniquely bittersweet — victory and grief in the same moment.

Why does it still generate debate?

The ambiguity of Lelouch's survival, the question of whether the Zero Requiem's peace will last, and the moral legitimacy of his entire project are all unresolved by design. Good finales don't close all the doors — they leave the most interesting ones open.