Complete freedom of choice.
In computer RPGs, you can only do what the program allows. Very severe limitations on being able to do things (limitations of programming) and express your character in whatever fashion (again, limitations of programming)
So, if you are playing NWN, say one of the taverns, you can only interact with certain characters in a very canned fashion and manipulate or interact with objects defined by the game program.
In freeform pen and paper, you could go over to the bartender and tell him that his mother dresses him funny and that his bright red shirt bemirches your ancestors. Then proceed to abruptly yank down his pants and hurl a chair or mug at the bouncer. The DM might look at you oddly but it is a your declared action and the DM will determine (usually by making you roll skill or attribute or attack rolls....or not) He tells you the outcome and then the roleplaying fun comes is dealing with the consequences of said actions. You will never get this level of interaction with a computer RPG.
Pen and paper RPG is collabrative story telling - you state what you want to do, the DM decides the outcome (sometimes with dice, sometimes not), you react to said information and everyone makes a story together (hopefully a fun and memorable one)