They are already working on a new IP so...problem solved?

The only thing stopping me from buying Shadow Fall at launch is that I'm already getting Battlefield 4. I'm not sure if I need to buy two multiplayer-centric first person shooters. I'll get Mercenary when it comes out though, my Vita needs something to play.

I disagree.

i'm pretty sure Killzone will be better then Killzone, but only by a small margin, they both gonna be great.

il get both
but i hope Shadow Fall is better

Both, Killzone is just awesome. Mercernary looks like it set standards pretty high on Vita

Isn't Killzone Mercenary designed to be like Unit 13? With Studio Cambridge involved as well, they're a good studio, but most of their games are low 80's score wise.

Meanwhile I expect Killzone SF to be reviewed extremely well with the buzz of being the PS4's big 'killer' launch exclusive (similar to what happened with Resistance FoM).

So Killzone > Killzone for me.

I would say Shadowfall. I just feel that the DualShock 4 and the work of the main studio instead of their new satellite should put them ahead

Personally, I wouldn't have released them both so close together, especially as they are set in different time periods

Anyway, I am buying them both, though probably only ShadowFall on its day 1

Somewhat. Single player is made up of a bunch of different smaller levels like Unit 13 but it still has an actual story. Also all of these levels can be played again trying to go for different achievements like stealth or sniping. Further more these levels trick the player into thinking things are linear even when there are completely different paths to take. Same concept as Unit 13, just executed much better.

Considering that the two PS3 games combined sold enough to pull in 200 to 300 million dollars depending on how many sold at $60, I'd say Sony  made their money back and then some on those two games. Few games take much more than 20 to 30 million to make and when we're talking single platform titles, it's typically less. Killzone 2's original budget was 20 million and after delays it eventually ballooned to 45 million. I can assure you, Sony still made a decent profit on that game and Killzone 3 likely made them more despite selling less since its budget didn't become as large as Killzone 2's. The Killzone franchise has established itself as THE FPS series for Sony. Unless a much better FPS is made or Killzone starts losing them money, there is no reason for Sony to stop the franchise. 

As far as which I think will do better? Killzone: Mercenary looks like it's going to be a great game but as it's on the Vita and FPS games seem to have a hard time doing well on portable platforms, I'd say Killzone: Shadow Fall is the safer bet for which will be the better game.