My year abroad in St Andrews was one of the absolute best of my life. I took four forth year English Literature courses and every one of them was absolutely brilliant. The professors and lecturers are some of the best in the UK and every one that I personally had were very enthusiastic about the subject they taught and were very engaged with their students. Depending on your discipline and the academic background you come from, St Andrews academics may be very challenging for you so come prepared to cram your brain full of knowledge and plan to become well acquainted with their well-stocked library.
Socially, St Andrews is very unique. If you're coming to study abroad in the fall or for the year you may have the option to be "adopted" by a third year into an academic family whose job it is to help integrate you into life in the town. You may become quite close with your academic family or you may learn from them what you need to know, get through Raisin and then choose to carve out a more independent path. I personally am still in close contact with my academic family even now after I've returned to America. Since St Andrews is about an hour away from the nightlife of Edinburgh, a very interactive array of student societies (or clubs as we call them in America) have sprung up over the years and there's never a lack of anything to do in town whether it be a themed night out at the pub with your society (Quidditch Pub Crawl with the Harry Potter Society is not to be missed!), a Bop in the Student Union, or a film playing. If you're not keen on extracurricular activities, there are usually a plethora of house parties, pub quizzes, and other things I'm sure you'll find your way into. The town has one tiny but veritable "night club" called The Lizard in the basement of one of the local hotels and you must go at least once just to experience it. If I had to pick one social highlight of my time in St Andrews though it would be the balls that are thrown periodically. Nothing is more fun and foreign from American college culture than dressing up in a glamorous dress or tuxedo and dancing the night away in some magical, classy location your fellow students have slaved over planning and setting up.
Since Scotland is a relatively small country and has amazing public transportation via trains and buses, it's quite easy to use your weekends to head north and explore its beautiful Highlands and Lochs, or take the train or a cheap 10 pound overnight Megabus from Edinburgh down to London. There are lots of cheap flights that fly out of Edinburgh to other European cities as well if you've got the time and cash to spare.
If you couldn't tell so far, I adored my time in St Andrews and it's made me greatly consider obtaining my post-graduate degree in Scotland just so I can go back. The only downsides that I heard my fellow Americans gripe about were the weather (it's very, very windy in St Andrews and sometimes rainy so pack accordingly!), the food (I quite like British cuisine but picky eaters sometimes find eating out difficult), and of course the dollar to pound conversion. I consider none of these deterrents though, and I hope you don't either!