I think the first original thing I ever did was a monster and for some reason, my standards for monsters have always been extremely high - I think it is partially because I found the xenomorph at a fairly young age - so young, that in my mind, it has always been there.
Although I don't believe anyone will ever top Giger's creation - there are still a few people out there, like Miyazaki and his team, who clearly understand monsters - and the Amygdala is the proof of that.
How do you create something that represents fear itself? You create the Amygdala.