I believe this is part of a free weekend promotion. If you already own the game, you might want to catch up on DLCs.
Note that the GOTY edition isn't complete. It only contains about half the DLCs, the older and free ones. Other companies have this annoying practice of releasing complete and GOTY editions which lack the newer DLCs or when addon cotent is still being produced. Crusader Kings 2 is an example.
What's the game like. I have PayPal 1 and 2, got them free with Ps+ but never looked ar them.