To keep the addicting Killzone 3 multiplayer alive, Sony is implementing something interesting. Next week the multiplayer version of Killzone 3 will be on PSN for free. Catch is - They will implement a level cap.
Once you hit the level cap, you'll have to pay up in order to unlock the full multiplayer. Again To unlock it, it will only cost you $15. Pretty good deal and a way better than getting the retail version of the game.
To me, this is a win-win. Not only does it prevent servers from being a ghost town, you get to try the best part of Killzone 3 for free, and if you like, go ahead and unlock it. I have Killzone 3, and the multiplayer mode is the saving grace of the game. The singleplayer, not so much. Sony is actually doing us a favor by removing the bad part of Killzone 3 and offering us the best part.
Again this is only for the multiplayer mode of Killzone 3. If you want to explore the single player campaign yourself, you'll have to get yourself a copy of the game.