I can't speak for the specific book you're talking about, but there are definitely a lot to say about relativity that has been discovered since the time of Eisenstein.

While it is true that more has been discovered about relativity since Einstein's time, that doesn't mean there isn't value in reading Einstein. When you approach an idea which is new to you, it's good to read something written for newcomers. When Einstein wrote, everyone was a newcomer. As such, his work is remarkably approachable considering how difficult the subject is.

While now I tend to think about special relativity using Minkowski space (which I find to be the easiest mental construct for me), my 12-year-old self found all that stuff in Einstein's Relativity about trains and clocks very helpful in building intuition about relativity.

As a counterpoint, I thought (and still think to this day) that the trains and clock stuff is hard to follow, but I understood it easily as soon as I saw it in terms of coordinates.

Not a lot, actually. Einstein (and a few other people before him) did pretty much all there was to it.