What makes these kind of particles interesting and "exotic" is that they are not the kind of particles the Standard Model was originally developed to describe.

What makes these kind of particles interesting and "exotic" is that they are not the kind of particles the Standard Model was originally developed to describe. Those particles, mesons and baryons, consist of two and three quarks, respectively, with some quantum numbers that must obey certain rules for the particles to exist, and we have found that (almost?) all of the two and three quark combinations allowed by the rules are in fact observable as particles in experiments. But those rules for the quantum numbers can also be fulfilled with certain combinations of four or five quarks, and there is nothing in the Standard Model that either forbids or requires these combinations to exist as real particles. So it was new information when the first resonances that could be interpreted as those kind of particles were discovered and it is interesting that there are more of these. But it is not unexpected, either, the earliest paper on pentaquarks cited on the wikipedia page is from 1987. So it is indeed close to business as usual. It is interesting, and new, but is is still filling out the corners of the Standard Model.