One reason is that fact that it shows how to learn Torah in a very simple and understandable way.
But also there is the fact that he (Rav Elazar Menachem Shach) was the only one to stand up and oppose the false god of the the cult that the Gra signed the excommunication on.
That already says a lot about the quality of his character and intelligence.
I should mention that the cult that the Gra signed the excommunication on change their story depending on whom they are talking to. They definitively serve a false god, not the God of Israel, but they get away with it because they are extraordinarily excellent in doing rituals. And to other groups that have obsessive compulsive needs to be doing ritual all day long this is a big plus. So they get a pass at serving a phony deity.
Of course there are levels of how bad things can be. This we see in the Eitz Chaim of Rabainu the Ari. The problem with the cult that the Gra signed the excommunication on is they worship the crown of darkness, the crown of the Sitra Achra. So their evil is not apparent. It is the higher root of evil.
The way I see things based on the Ari is there are planes of evil. Not all evil is the same. The root --or from where evil comes from is not the same as the evil itself. And I do see it as a metaphysical reality. See the part of the Eitz Chaim after Shar HaNukva and you will see what I mean.
Appendix: Just to get back to Rav Shach. The point of the whole school of the Litvak Gedolim was global. It was to understand how the subject in front of you fits with the rest of Shas and with the Rambam. The trouble is that most of that school is hard to understand. It is easy to finish an essay of Reb Chaim Soloveitchik and think you still do not get it. With Rav Shach, that never happens. He makes the deepest concepts crystal clear.