i found law school to be just as difficult as engineering, but in a totally different way. it was a lot more work, for one thing.
so far, i have no regrets. studying for the bar exam sucks, but it's not unbearable. i didn't like my engineering job (which really ended up being a lot more project management than actual engineering); i suppose if i had been in a more technically rigorous position i might have found it more rewarding. but from my (so far) limited IP law experience, it's looking to be a pretty challenging endeavor.
i will say that if you think you might want to go to grad school, it will only help your legal prospects later. you could also always take the patent bar and find work as a patent agent; that way you could get a little insight into the IP life without the all-in plunge of law school. with an advanced EE degree and a PTO registration #, you could find work as a patent agent pretty easily, i'd think.
as far as lawyers being miserable, i think it's partially a function of the lawyer personality, and partially a function of people being stuck (or so they think) in firms that arne't good fits for them. i know plenty of lawyers who like their jobs...IP attorneys in particular. any legal job is a lot of work, but then again, 40 hours at a crappy job can kill you a lot faster than 55 at an interesting, challenging one.