Oud is exceptional. I highly recommend anyone wanting to explore beyond western perfumes to check out www.ensaroud.com - there's some really fantastic descriptions of olfactory notes too.
The bloom and trail effect given by ambergris is replaced with ambroxan, however combining ambroxan and ambrinol does little to recreate a "real" ambergris odour. Those may thousands of other molecules, while perhaps only <5%, give a very distinctive and unique odour. It's like a rich leather bag that's been floating in the ocean for +30y - salty, marine, animalistic, musky and leathery all in one.