Coming from someone with a masters in engineering, I'd say that from what I've heard/read about law school, Law school will likely be more intense than my grad school experience.
Keep in mind as others have suggested that grad school experience can vary significantly. Even in my engineering department some grad students coasted along while others were hurting from work, etc. A lot depends on your thesis topic and the professor. Like law school, perhaps even more so, the professor is a big factor in the experience. Itís not uncommon to be working (teaching a class), doing research and taking classes with the same professor.