These are definitely NOT light muffins. These are a very good banana and chocolate chip muffin. The espresso flavor is there, it's not very significant though. I think it just gives it a deeper, dark flavor. Nice.
I find that my espresso powder (pictured in the background) has come in handy for a few recipes. I've used it in brownie recipes, an ice cream, and now these muffins. It also came in handy during a blizzard when we ran out of coffee. I made espresso- mine diluted with a bit of cream and sugar :)