if you could only get one game and it not be a sports game, get AC4.
after that I'd go either NBA 2k14 or Fifa 14 depending on which you like more, because they are both better than Madden and you can get a lot of time out of them for your money. so trade Madden if possible lol
the third game imo would be Need For Speed: Rivals because it looks amazing, has a lot to do in it, and the multiplayer is integrated seamlessly. I bet this game would be a blast with a lobby full of friends.
the fourth game would be an obligatory multiplayer shooter. Ghosts is pretty much for sure in 3rd place out of the 3. Killzone is an exclusive, and the multiplayer is a blast. The single player is less cookie cutter than Battlefield's, but I enjoyed BF4's more. Personally, I really think the KZ multiplayer is better and it is the better game. However, the population thus far online has been tiny compared to BF4's. Maybe there will be more people after Christmas? Tough choice between BF4 and KZ.
Games to rent b/c you can beat them before returning so why buy?: Knack every shooter's campaign on this console