i changed in the following ways (and most of my friends did too):
1- a love of Israel, and the Jewish people. Its a wonderful feeling that stays with you throughout the rest of your life.
2- Understanding and accepting people from different backgrounds. I met girls in my seminary who became super frum, and others who were struggling to keep kosher. I learned that we all have a lot in common, and to see everyone for who they are (i.e. less judging)
3- Its a fun year, a gap year, to do whatever you’d like–the country is yours 🙂 After this, you’ll probably be studying in college, and you could probably use a break
4-it did worlds for my connection with Hashem–He is so tangible in Israel.
And many other ways….