My humble opinion. The Gorilla advert worked because it was unexpected and original (and Phil Collins is the friend of everyone's Mum and Dad).
This advert whilst visually beautiful and audio inspired fails to deliver the brand message and differentiation in a packed market place Cadbury's were attempting to achieve.
In short it would be original and impactful if it was not for its predecessor, unfortunately it is now watered down by being a bit of a gimmic.
A vicitm of its own success -