Shell accounts are easier to set up and access than PPP accounts, since they require little or no specialized software running in your computer. They can be accessed with as little as a simple terminal and a modem. They can be harder to use, however, since most people are not experienced at using the Unix operating system from a command line interpreter. Also, since the only commonly available terminals were once text only displays, shell accounts are usually limited to text only, sometimes in color, but without graphic imaging capability.
Modern computers will often provide a Graphical User Interface (GUI, pronounced "gooey"), usually a windowing system, as thier primary human interface. Xerox is usually credited with pioneering this approach with their GEM windowing system.