Killzone: Shadows Fall, no questions at all, especially since all the previews hit yesterday.
Revision 3 Video Preview
IGN Video Preview
It is looking pretty damn amazing for a launch title, and both the preview videos above go into how they are taking a more open approach to the level design, so you have to get from point A to B, but now there will be several options for doing so, along the lines of Crysis 1 is the comparison that is made in one of those video previews above.
So yeah, I do not even think it is a question, this is the launch game you want to pick up for the PS4.
I also say Resogun for a downloadable title.