One of the differences between them is the speed, PHP7 is faster, needs less servers, the codes run super quickly.
Another plus is that you can use base exceptions, so you can get rid of catchable errors.
Something really cool is that you can run it as always on Linux, but this one is also supported on Windows
You can use anonymous classes, so better execution obviously.
Basically what you will notice is the increase of the speed and the performance, has some new features like the spaceship operator, and the null coalesce operator.
It has some issues with backwards compatibility though, but definitively is not due to its design.