1. The structure of the curriculum is different between Belgium in the U.S. In Belgium, law is studied for a period of 5 years straight after high school (secondary school). In the US, law is studied after completing undergraduate studies (usually 4 years) and lasts for 3 years for a total of 7 years before becoming a lawyer.
2. Choosing a university in the U.S. is a challenging experience for two reasons. First, many American university usually specializes in certain areas of law. Second, some American law schools are more prestigious than others. In contrast, Belgian universities tend to be more general and the ranking plays little (if any) part in the popularity of the university. This means that Belgian candidates probably opt for universities that they have heard the name of (i.e. Harvard and Yale) at the expense of other excellent universities and regardless of their specialization. This is why it is important to do your research to find the right law program for you.
3. The interaction between academics and students is also different. Belgian students generally address the academic staff formally, almost never discuss personal aspects, never meet for social events, or call a teacher by his first name (even if they have known each other for several years). The U.S. tends to be a bit more relaxed.
4. A law degree in the U.S. does not entitle one to practice law. The person holding a JD must then pass the Bar exam in the state in which he wishes to practice law. There is no such thing as bar exam in Belgium; upon completing 5 years of law school, one is entitled to practice law and become a Member of the bar (e.g. Brussels Bar). Potential candidates must be aware of the fact that completing a LLM in the U.S. will not necessarily entitle them to practice law in the US afterwards. Only a very limited number of states (usually NY and California) make foreign lawyers eligible to sit the bar exam.
5. The marking (grading) system is significantly different. Belgian students may be reluctant to study in the U.S. and spend a large amount of money because they think they might fail the course; thereby earning no qualifications. This is because, under the Belgian system, a significant number of Belgian students fail to pass their exams and sometimes simply give up after studying law for e.g. 2 years or have to repeat a year (i.e. complete their studies in 6 years as opposed to 5). There is no such thing in the U.S. and any Belgian candidate must be aware that the failing rates are very different in the U.S. than in Belgium.