It's easy really, just let the Helghast and ISA join forces to fight a invading army of cybernetically enhanced super soldiers in green power suits.

Uh, they already did that in Killzone 3. Jetpacks and armor suits. BTW, I LOVED Killzone 3. Really fun game. Killzone SF? Not fun. Beautiful but soul less.

They need to realize its not just about shooting and looking pretty. You need to have a universe to have great stories, which is why Mass Effect and Halo are critical successes. Plenty of back story and material to work with.

Honestly? For it to be a massive hit, they would have to dumb it down. Make it less subtle and political. Most people can't deal with a conflict where both sides are corrupt, greedy, and ruthless. They want an ACTION HERO(!), on the side of RAINBOWS AND JUSTICE, who is out there shooting bad guys and aliens--especially aliens because they're not human and are thus mindless, evil scum. That would make me sad, as the standard "Starship Trooper" fare leaves me cold, but that's what makes a hit.

Killzone also suffers form what I call "Final Fantasy Syndrome" where previous installments have fragmented the fanbase by being different from one another. You have people who loved KZ2 style and others who hate KZ2 style and neither one will be happy with compromise. There are a LOT of gamers out there who are unable to judge a game by its own merits and instead constantly compare it to previous games.

I don't want Killzone to end but, honestly, to appeal to the mass market, they might need to try something more simplistic, with a marketable "hero" and clearly defined "good" and "bad" guys. As a person who reads a lot and loves complex universes, that makes me very unhappy to say, but that's where the money is at. Generic sells.

It would appear that you know absolutely nothing about the Killzone universe.  No back story?  Seriously?

That kind of annoys me.

Let Naughty Dog make the story and have them consult on the game design

XD

What is the back story? Shadow Fall will be the first one I get so I'm worried I won't get what is going on. Do you need to know what happens in the first 3?

I would buy 72 copies of this game, even though I don't have a PS4.

To make the game a success you need more people to play the game, reviews are secondary...word of mouth matters. Sony having a much bigger first party collection of studios should leverage this advantage over the other console makers.

This would be my strategy....
Release a game at retail e.g. Game A 1and let it run. Follow up with the usual DLC stuff etc to milk the franchise.
A year later release the sequel Game A 2 but the same time make Game A free to play (minus dlc).

Advantages - longevity of Game A 1 is increased, possibility of extra revenue from dlc, possibility of capturing fans for the franchise and knock on sales for Game A 2
Disadvantages - no revenue from sales of core Game A 1. Sales will also taper off faster as a sequel is announced and know Sony will do this.

This what I wished sony had done with a game like warhawk. So far into its life there was apparently still a strong community (or maybe still is) going and Sony could have added to this by making it free to play. They would have even make money out of free to play through dlc.

Anyway thats one way to make a success (i think)....

No, you actually don't, as Shadowfall skips into the future after KZ3 and kind of starts its own storyline.

As for the KZ universe and backstory, which the first three games actually didn't get into much, it's all about greed and power.  Basically, the good guys aren't so good and the bad guys are actually somewhat justified.  The Helghast tried to break away from Earth's control but the government didn't want to lose all those valuable resources and profits, so they made an example out of the Helghast.  The crushed them and exiled them on a harsh planet, where they became strong, brutal, and bent on revenge.  It's a story with a lot of parallels with our world.  It's meant to be realistic and political.