I've got to watch it a second time. First reaction was that it was a little underwhelming. But maybe it's just because it wasn't what I expected.
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"Why did he want revenge on his brother so much that he would kill himself to get?"
Was it revenge? Maybe it as a noble act - taking out himself and Amon so that they could no longer cause harm. As he said, he didn't want to seek vengeance for his father - but he did anyway. Maybe he was preventing that from happening again?