It's like college in terms of the assigned work load. The big difference is that you have to actually do the work in law school, and you have to do it well (ie can't skim through much, and have to take notes on what you read). Another big difference is that the professors call on you, and make you answer questions that range from easy to impossible. This can be stressful.
In terms of the atmosphere... I went to a large university (17,000 undergrads). Law school (my class has 240) is very much like high school. People are a little more mature, but there is still a bit of gossip, cliques, etc. Generally people are pretty nice though.
Exams in law school are no fun at all. They count for 100% of one's grade, and hard work doesn't necessarily pay off (after all, everyone is working hard, and not everyone can be at the top).