Almost all of my friends go there. It's a good place I guess. Small, beautiful city center, lots of activities to do for students (parties every night, bars everywhere, free gym, swimming, a skatepark that's really hard to skate..).
As far as the school goes, it's a very good one. Dozens of campuses, thousands of students. Basically everyone in Leuven during the week is a student, it's really a student-city.
I have a personal dislike for it, as basically everyone around here wants to go study in Leuven just for the partylife, they don't seem to care what they're going to learn. It's a very good place, but highly overrated, not that you should care about that though.
A semester in Belgium will be a lot cheaper than Sweden or Switzerland too. A beer in Leuven costs ?1, in Sweden that's like ?5 or something.