M-x shell is one of the first things I just show people when I introduce them to Emacs. I had a databases class a few years ago where the CLI program we used to interact with the database was a basically an input loop where you entered commands. It had absolutely no concept of history though so if you messed up a query you had to retype it or use the clunky copy and paste feature of whatever terminal emulator you were using. Emacs changed everything though be cause I could just kill my last command and paste it into the new prompt. I have since done this with many other commands and I love it.