I am researching the music of the last 30 years in order to write a chapter about it. I have already compiled and am working on a list of operas. See here.
Minimalism descends from the avant garde of the 1950's and is led by Steve Reich, Philip Glass and Terry Riley. The first and last of these three I am familiar with through listening to the recordings of the Kronos Quartet. Kronos used to rehearse in the school near my house in Berkeley. I am a big fan of Kronos.
An early landmark is Steve Reich's "Drumming," 1970-71. Which I have heard. It's, what can I say, it's ... a lot of drumming. Not percussion, just drumming. How more minimal can you get? There used to be people who jammed on drums for hours on end on the cement stairs on the Bay at the head of Hyde Street. You could join in if you brought your own drum. They sort of swung, if I recall correctly. Reich is just drumming.
Some of his early stuff is actually tape manipulations of people talking, which I consider more avant garde than minimalist. Glass is the most minimal of the minimalists. He just does simple triads and arpeggios over and over until your mind goes completely numb.
I have been investigating the work of Arvo Pärt recently and find him repetitive. [Insert laughter here.] That is a gag line. If I have to explain it, it isn't funny. He is doing antique textures--Schütz or Perotin--with modern harmony. It generally has a religious context, and is in fact, intensely religious.
The rest of the group of minimalists are John Adams (not so minimal), Le Monte Young, Meredith Monk, Sol Lewitt, Donald Judd, Carl Andre, Richard Serra and Bruce Nauman. Except for Adams, I can't tell you anything about these guys.
It is possible to get your brain around the music of the minimalist school which makes them a huge improvement over most of serialism. Less is more.