Simply put, if you haven't experienced Mass Effect then you really haven't entered the "now" generation. From its incredible scale to its dialogue to the wonderfully written characters and themes, Mass Effect is a golden god. You are Commander Shepard, charged with freeing the galaxy from an evil rougue specter named Saren. It is this course of action that leads to an incredible ending that I won't spoil.
Inventory can get a little clustered, mild frame dips (nothing serious), side missions get repeated a little.
All in all amazing.