Greeks are most visible when they're rushing recruits. You'll see them at their booths in the Library Quad during the first two weeks of school. After that, they disappear from the spotlight. How much they impact your social life depends on who you hang out with, because honestly, they're really easy to avoid. Not that people avoid them on purpose; it's just that a minority of students belongs to fraternities or sororities, so they can fade into the background. Greeks are very happy and vibrant within their own communities, and their members swear by them, so they must be doing something right. Non-Greek students don't really pay attention to them, though. There's no Greek row housing, which undercuts their influence. Again, because Sac State is a commuter school, it's pretty easy to get away from on-campus forces like the Greeks. If everyone lived at school, they would be nigh impossible to escape. Panhellenic pandemonium exists, but students must seek it out.
A major reason students shun Greek life is the pay requirement, but that's about it. Some people are more quiet and introverted, and others think Greeks are just too superficial. If you want into a fraternity or sorority, just fork over some cash and start socializing. You don't have to give up your soul, though: just some dollar bills.