For those in the Greek system, being Greek is a big thing—it dominates your social scene. But frats and sororities tend to associate with everybody, even non-Greeks. If you want to join, there are enough so you can find one that suits your interests and personality. Greeks are active in many events, but there are also many opportunities for non-Greeks to be active on campus. If you want to join an organization where it is easy to have an active role, then Greek life is one choice.
Greek house parties and events are typically open to anyone who wanders in. If the parties are what you are looking for, joining is not necessary. Being in a frat or sorority may help you make friends quickly at the beginning, but it may limit your social encounters with the non-Greek population. Make sure you research the different societies and visit them before you decide which one to pledge. It can be hard to keep up on academics and participate in all of the social activities required, so understand the time commitment of the society. Overall, those who enjoy Greek life will enjoy Iowa State, but those who don't wish to participate will equally enjoy their time at Iowa State.