In case this helps - my D started at Vassar this fall. She is somewhat of an introvert, not a party type, with interests in the Social Sciences/Humanities and Theater. It has been less than a couple of months - she is very happy at Vassar. She describes the students as kind, helpful and accepting (both incoming first year students and seniors). Seniors have reached out to her proactively to ease her transition. She was able to get involved in activities very quickly, and has formed multiple groups of friends.
Academically, the classes are engaging, the professors very accessible. The workload is rigorous and keeps her very busy. It is a collaborative environment with smart, driven students who are eager to help each other out, form study groups etc.
Based on my D’s experience so far, Vassar would be a good fit for your son.