In 2014, mankind successfully landed its first spacecraft on a comet. A lander known as Philae was landed on comet 67P, and although the landing didn't go as smoothly as hoped, we still were able to gather a truckload of data to learn more about comets.
One of the things we learned are that the surfaces of comets are probably harder than originally thought. Rock solid ice was detected when scientists evaluated the noise from the bounce when Philae landed incorrectly on the comet.
Moreover, Philae detected many organic compounds on the comet, including acetone, propionaldehyde, methyl isocyanate, and formaldehyde. In its search for life, the lander even found water on 67P, but the chemical makeup of the water wasn't quite the same as here on Earth, so it helped us realize that comets probably weren't the bringers of life to Earth.
Other things we learned about are the presence of molecular oxygen on the comet, which was a big finding being that molecular oxygen has only been discovered twice outside of our solar system, and that comets may pre-date our own solar system.
Indeed comets are strange pieces of the universe, but their presence is something that needs much more investigation to fully understand.