1.6 relies on community hosted servers, 2 relies primarily on centralized servers and queueing mechanism. There are changes to core maps. Changes to weapons. 2 very much has the features you would expect from a modern game. 1.6 is very bare bones, but highly customizable through addons; each server can install their own addons and make the user experience unique. Hopefully this 1.6 remake will keep the server customizability intact.