Is there such a thing as too much crema on espresso?

I buy fresh beans of lighter roasts, grind a few minutes before extraction, pull a double shot normale, and end up with a lot of crema, I mean a lot!

Right when I'm done, the top 90% of the shot is crema moving around like the head on a fresh Guinness. After it dissipates for 30-60 seconds, I'm left with roughly a centimeter of crema of light color.

Crema is a pretty bitter flavor, so I wonder if there is something I'm doing to cause this type of extraction, if it's actually a good or bad thing, and what I can do to improve on my technique?

Cheers!