1)The CD key
Single player games:
_ 1 time activation for single player games, not liked by the crowd, but it takes care of (not liked by the crowed, but if there is a multiplayer element, people will not care about this), this takes care of used sales.... and it's a one time thing.
_ Always online... not liked at all by the crowd, not compatible to consoles as 1/2 the market share would be taken out.
_ No online necessary : does not prevent anything... but the action of using a CD key many times is as illegal as a pirated copy... and for a pirated copy, there won't be protection anyways. (on the plus side, it lets people lend their game and not feel bad).
Multiplayer games:
_ works fine for Valve and Bliz... people don't care as you're online anyways.
Added advantages:
No need for CD protection (that gets pirated anyways)
Can have no CD install (++ for the crowd)
In order to control price, you could have the physical game cost 5$ and the CD key sold online at the publisher for full price... easy and cheap.
-> this would allow for used sales... sortoff... but you could modulate the resell value by changing the physical game price.
EA kind of went this way with their 15$/10$ online activation.
Problems
... if you sell CD keys as a standalone, you legitimize pirated copies (hence why I lowered the premium).
... pirated copies of single player and illegal multiplayer servers.
-> CD key linked to an account.
same but even better as it's transferable between your consoles/computers....
Though for the customer, this means no resell value (you can resell your cd key... to friends as they can assume you won't use it anymore) and no lending to friends.
-> the other way is free DLC
Why does this work? because people feel the item they buy used or pirate does not have the same value... only problem is that this content can be pirated too.... but in the end, people who buy used because it's cheaper... will likely keep on buying used....
-> unlockable content
Same as free DLC, but concerns key elements of the game.... People who buy used will actually feel cheated and resent the company more than the seller... this would lead to bad PR.
-> locked on one console
Isn't that basicaly using a CD key? but in more complicated as each CD needs to have a specific ID... Plus imagine if your console breaks... Much better to have linked to an account than a console... But you could add console linked to an account... that would take care of the console breaks part. (isn't that Itunes?)
I prefer the CD key