I suppose it’s a very intense short-lived experience due to the size of the beverage and how the texture is layered.
So you get the first sip: creamy, bitter, velvety, intense… And as it cools down and the crema dissipates, you get a more thinner, sweet beverage.
Try mixing the crema in - essentially stirring your espresso and see if you then get a more uniform flavour.
Remember: Stirred, not shaken. 🙃