What are the most popular student activities/groups?
Dances are often held as fundraisers, which tend to be the most popular (and successful) student events on campus. Theater and music, especially a capella, are also overflowing on campus. I am active in Relay for Life, an annual fundraiser for cancer research. This event is always packed with students. It's really nice to see that different groups on campus come together for such an awesome cause. Writing is also prevalent on campus. I am a copy editor for a weekly newspaper called The Justice. There is another paper, The Hoot, which is also weekly.
Greek life exists but the fraternities and sororities aren't officially recognized by the university. Because of this, the houses (and the parties) are located off campus. Basically, it's there if you're interested and it's not a big deal if you're not. Greek life definitely doesn't take over the school.
Being close to Boston is great, but most students stay on campus during the weekends. There is so much to do on campus! It nice to have the city as a get away if Waltham ever gets to feel too small (it happens).