I thought it was one of the coolest things announced at E3, being able to play with your friends on Far Cry 4 even if you don't own a copy, and vice versa. That's a great feature and I hope more games utilize it in the future. If I remember correctly Microsoft wanted to do something similar with their original XBO design but they dropped the idea when they removed the DRM. I'm happy Sony is testing it out. 

The DS was doing that before it was cool

Mystro-Sama said: The DS was doing that before it was cool

Same with the PSP, I played Killzone Liberation like that with friends.

OT. Yeah that's a great feature, there was a thread on Neogaf that said Sony is looking to make this feature standard on hardware wide level. Will try to find it.

It's a cool feature that should be standard. However, I don't see too many developers taking advantage of this, since they'll want to bilk as many people as possible into buying the games. I'm surprised this hasn't been at least somewhat more common, though--Dr. Mario Online RX on the original Wii had this feature, too.

because sharing games was around before the Playstation existed. lol

I thought the Far Cry 4 co-op idea was cool. However it seems what you get is a couple of free trial keys.

"PSN Exclusive: Keys to Kyrat

Invite your PSN friends to join you in the open-world, even if they don’t own the game. The PlayStation exclusive Keys to Kyrat includes free passes for online co-op trial, allowing you to capture outposts together, hunt and craft in the open-world, and gain experience and money with any of your PSN friends." from FC4 Website (http://far-cry.ubi.com/en-us/)

Actually, sony is making it a platform wide feature. So in the future every game that can support it will. There is an interview dancing around confirming this. Apparently its part of what they announced when the revealed the PS4 back in feb last year.

And I personally see publishing jumping onto this thing. Its a great way to increase the sales of your game. Imagine a game like tekken, and you can only play tekken when i invite you to play, or a game like Destiny, you can only play multiplayer when I invite you. You come in, play it... get hooked, want to play more but I am not there to invite you all the time. What do you do? Go and buy the bloody game. Its a good way to get people that didnt plan on buying a game to actually play it and get hooked.

EDIT: here found the link

"Keys to Kyrat" is the name of the system (or exclusive DLC, if you wanna call it that),it's not a "key"/code

While it is a cool feature it has been done before. Though to do so for a AAA title like FC4 is somewhat special in that regard. I know someone on my friends list will pick it up and then I can demo it while they play.

You obviously don't know how this sytem works.