Disclaimer: I an Alien girl, the original is my signature, and so far I have loved all of the flankers that I've smelled, too. So I am definitely partial. With that in mind, I agree with the previous reviewers. This is essentially a richer, more mature and rounded Alien, not to mention more expensive and with a narrower product range.
For me, the vanilla is instantly discernible amid the blast of jasmine, but the jasmine subsides a lot faster than in the original, giving way to the softer, deeper notes. Wood and amber are there, and apparently incense, myrrh and orris root as well in the best oriental tradition. It lacks the original Alien's occasional harshness, but is not for the faint of heart either: at least for me, it drowns out other perfumes easily. An excellent autumn/winter scent.
I generally like flankers when they are well made, because I like having different takes on my favourite fragrances to wear for different occasions without having to deviate from my signature. If you were underwhelmed or repulsed by the original, you probably won't care for this one, either. In the end this perfume rises and falls with Alien. I love both, but not enough to warrant buying both as full bottles. Essence Absolue is a close contender with the original for a permanent place in my closet.