Most psychology textbooks assert that there are seven basic "psychological changes" that have to happen during late adolescence (or during the "college years" as your question asks). It is important to talk about what those psychological changes ARE before we can talk about "what college-environment characteristics" will contribute to those changes. The seven changes are as follows: proficiency in study, management of emotions, autonomy, "finding oneself" or grasping identity, varied relationships, determining life's purpose, and establishing integrity in all of the above.
First, proficiency in study does have a bit to do with personality (as well as factors such as ADHD and such), but in regards to how the "college-environment" can help, the college can provide ample study space in various ways. Some students study better in groups, so group study areas should be provided. Some students need constant guidance, so tutoring programs (such as in the library) might be useful. Many students, however, simply need solitary quiet for studying, so small, comfortable study rooms (for one or two) should be numerous.
Second, in regards to managing one's emotions in late adolescence, there should always be both a counselor and a nurse on hand at all times. Depending on the college size, there should perhaps even be more than one. It is often that college students just need someone to talk to about friends and lovers who can remain objective. A counselor is a perfect medium. Sometimes the management of emotions enters the health field in regards to medication, however, (and also in regards to more serious psychological issues such as suicidal thoughts), so that is why a medical staff is important. Further, in some ways, a counselor would be helpful in many of the other psychological changes as well (such as for finding a job or talking about possibilities for the future). Finally, it's also good for a college to have student support groups in case the student wants to talk with objective peers about emotions.
Next, autonomy is best explored in the actual decision not only to go to college but also to LIVE at the college. There is less autonomy afforded to student who commute from home. (I have seen this first hand.) For this reason, there must be ample, comfortable dorm space for all students who want to stay on campus. There should also be varied types of room situations, such as co-ed dorms, single-sex dorms, rooms for 1 or 2 or 3. There should be options with a hall bath and options with suites. There should be dorms for honor students, dorms for fraternities and sororities, and dorms for other special clubs and groups. Housing should be plentiful and afford many options for the best experience of autonomy.
Fourth, grasping one's identity or "finding oneself" has a lot to do with electives (ESPECIALLY foreign study), student clubs, peer mentoring, and faculty mentoring (in addition to various social activities). Students have to have ample opportunity to take classes out of their original comfort zone. Try geology and astronomy. Take a class on Victorian literature. Visit the Holy Land. Learn about Elizabeth the I of England. Read the Koran. In addition to finding new interests this way, there have to be many clubs to choose from that will spark student interest. Everything from science clubs to sporting clubs to social clubs to poetry readings need to be explored. Further, mentoring must be offered, not only in the student's chosen field of study (faculty mentoring) but also in all other issues of student life (peer mentoring). And, again, when drastic emotions pop up in regards to identity, a professional counselor needs to be on hand to help.
Next, students having varied relationships is almost a given. Students need to be free to explore friendships, work relationships, student-teacher relationships, romantic relationships, etc. Almost every type of relationship will be afforded to them in college, whether the college tries or not. Many psychologists thinks learning about relationships comes in three steps:
First, one moves from valuing relationships based on need (dependence) to valuing individual differences in people.
Next, the person learns how to negotiate those differences in relationships.
Finally, the young person begins to understand the need for interdependence and seeks mutual benefit from relationships.
Sometimes I wonder, however, if whether the so called "party schools" are really called such because they focus more on student social relationships (i.e. this one aspect of student fulfillment) more than others.
Further, we need to speak a bit about determining life's purpose and the virtue of integrity. I am grouping these two together because a faculty mentor can be of great help in this arena (even in the simple step of keeping those appointments). Further, student opportunity for religious exploration needs to be afforded to them. Services for all faiths: Catholic, Protestant, Muslim, Jewish, Buddhist, etc. must all be represented. In fact, EVERY SINGLE RELIGION present in the student body should be fostered. Some colleges explore integrity in the form of an "honor code," which allows students to take tests in the comfort of their dorm rooms while they promise not to cheat. We could also revisit our other paragraphs here because taking electives also serve as a good way to determine hobbies (and even life-occupations) that one might not expect.
As you can see, there are many ways colleges can provide a favorable environment for the seven major psychological changes that college students face. The question arises as to how to find the right school, or even, how to find the school that has a good focus on ALL of these. The answer is research. Know a bit about yourself before you choose your college. If your focus is art, then don't choose MIT. However, probably the best way to find out the answers to your questions is to VISIT and ASK STUDENTS (and not just the ones hired to give the tours)! Trust me, they will be VERY happy to share with you the best and the worst of their school! This kind of field research will lead you the closest to happiness during the college years.