Phenomenal. Before I got them, I had some really average pair of earphones. I knew they just weren't good enough though, because the audio couldn't really deliver the crisp, detailed sound that Sennheiser have.
I have used a number of Sennheiser products over the years when setting up and operating sound desks. I chose the Momentum In-Ear product confident that it would produce the same high quality of sound that I have come to expect from Sennheiser. I was not disappointed. This is yet another excellent product from Sennheiser.