It is undeniable that the Greeks play a major role at Vanderbilt. A lot of people are frustrated with this and like to come down on the Greeks and call them sheep or people who buy friends. It is easy to be negative about the Greek system because it is so prevalent, but because all the parties are open to everyone and there is an honest sense of inclusion, the Greeks provide a really good service to the community in planning and organizing parties and events that everyone else can benefit from (even if they're not in a house).
The pressure to join a fraternity or sorority is definitely there. Obviously, a large part of being in a fraternity or sorority is bringing in the next class of people. As a result, the Greeks are really inviting to freshmen and do their best to recruit them into joining their specific house. While the Greek system does provide you with a good group of close friends, it is important to realize that after you get settled into a house (or decide not to rush), you'll likely be hanging out with the same group of friends anyway. Classifications aren't as big a deal as you once thought.