Higher precision measurements will determine whether what is seen is indeed a peak of the right form. In fact, the second peak may be low in part because of the physics of inflation. We expect in many inflationary models that the small scale density ripples are slightly smaller in amplitude than the large scale ripples. The higher peaks will also tell us about conditions in the Universe when it was in its infancy. These patterns formed by the sound waves can be used much like ultrasound.
Ordinary matter loads down the oscillations of the photons, like putting weight on a spring.
The result is that the second peak is suppressed relative to the first and third. There are other possible explanations of the low second peak but in my mind the most likely one is a combination of the above two effects. This situation will be resolved if and when we see the third peak. I've seen what's on second. The location of the first peak in the power spectrum provides the best measure of the curvature of the Universe, and hence the total amount of matter in the Universe.