How have our laws changed from the last 400 years?

There have been huge changes, more than I can possibly describe here. Here are a few examples:

1. The adversarial criminal trial (a trial before a jury in which the defendant and the prosecutor present evidence, examine witnesses and (usually) have lawyers) - this method of trial developed in the early to mid 18th century

2. Copyright law (beginning with the Statute of Anne In 1709)

3. The end of statutory religious discrimination (400 years ago, religion and state were tied together, not following the state religion resulted in disenfranchisement and persecution)

4. The legal treatment of women has changed (from virtual property to legally protected equals)

5. Land law has been massively reformed (with the abolition of many feudal forms of land ownership)

6. Negligence has become a generalize cause of action, rather than a special liability limited to particular cases

7. In Civil Procedure, the writ system has been all but abolished and replaced with a modern code of civil procedure.

8. Various aspects of substantive criminal law have been codified, starting with the Offenses Against the Person Act 1861.

9. The rise of Democracy (400 years ago, few people had the vote and politics was extremely corrupt and controlled principally by the aristocracy. This didn't change until the mid 19th century).

10. The rise of criminal appeals (until the very end of the 19th century, criminal appeals were extremely rare and difficult)

There are full articles (and books) out there about it. Lots has happened, including the American and French Revolutions.

A jury of your peers is "new". Used to be just a judge (who was rarely impartial) or even the king.

Trial by combat is no longer acceptable.