Tough stuff. Unless you're one of those super-geniuses, I'd advise against taking more than one class that meets every day (most classes meet two to three times a week), as I did my freshman year. However, just in case four classes isn't enough to keep you busy, you can tack on a fifth. There are no credit hours, which makes scheduling simple enough: pick four classes and go.
Also, there are a lot of Econ majors, Psych majors and English majors.
My favorite class turned out to be, surprisingly, Japanese, which was also one of the hardest classes I could have chosen. As a result of loving this class, I became an Asian Studies major... something I could not have forecast as a freshman. It seems to be working out well, though, and I find the classes within the department are very strong, and the professors are very helpful. I had a class of 12 students my freshman year, which dropped to 8 my sophomore year, and was divided into two parts for half the week, so I had a class of 4. This did wonders for increasing my language conversation ability, though, and worked out well when I got to go to Japan. We also have sushi parties outside of class, where we make our own rolls and play DDR... awkwardness at its best.
One of the most unique classes I've taken was probably "The Embodied Mind"... an interdisciplinary look at ways of explaining the mind and how it works, looking at it through Buddhism, Neuroscience and Philosophy. It met once a week, and supposedly encouraged meditative practice, but we weren't graded on it so it unfortunately became obsolete. I took the class in its beginning stages, and doubtless it will improve as time goes on, but it was nevertheless a very interesting course, and its greatest strength was probably the diversity of views it aimed to present.
I'm glad Williams has athletic requirements, since it's an added motivation to stay active throughout the semester, and there are a lot of good PE class offerings, including dance, yoga and independent weight training.
I guess it's worth mentioning that I've never felt so overwhelmed and in over my head as I did my freshman year at Williams, thanks to the rigorous academics. It caused a real identity crisis and miserable social life for my first year... but getting through it was one of the best opportunities for growth that I've had. Williams students do (occasionally) have intellectual discussions outside of class, and sometimes the discussions in class are awesome as well. Sometimes they're not, but that's luck of the draw. Since classes are small discussion is easily fostered, and ultimately I'm incredibly proud of Williams' academics.