By your own admittance you haven't played the game! Played single-player its still DS as you remember it, it really isn't Army Of Two in Dead Space pants.
Don't judge the game by the demo either, what appears as a continuous stretch of play in that thing is actually a 2-3hr stretch of mid-game with all the quiet, tense moments cut out.
I swear, when people pick this up from the bomba-bin in a few months time they are going to be quite pleasantly surprised.
I've been watching an LP of DS3 and it seems a lot more action-y than DS1 or DS2. In fact a lot of the missions seem pretty lazy, and generally involve lots of backtracking while being forced to fight wave upon wave of enemies:
Ellie: Get to the shuttle Isaac!
Isaac: OK I'm here.
Ellie: Damn, there's no fuel in the shuttle. Find the fuel pump and fill up the shuttle!
*spend 30 minutes fighting your way to the fuel pump, activating it, then fighting your way back to the shuttle*
Isaac: OK the shuttle is fueled. Let's get moving.
Ellie: Damn, there's some debris blocking the train. Go unblock the debris Isaac!
*spend 30 minutes fighting your way back the way you came, entering a slightly different room, solving a puzzle, then fighting your way back to the shuttle*
Isaac: OK the debris is unblocked. Can I get on the train now?
Ellie: Let me test fire this shuttle first. Get somewhere safe.
*fight your way out of the same area and get somewhere safe*
Isaac: OK I'm safe now.
Ellie: Uh oh I accidentally launched the shuttle and I can't stop it. GET BACK TO THE SHUTTLE BEFORE IT'S TOO LATE!! Oh also there is now fire everywhere that will burn you to a crisp if you touch it. And every monster on the ship has just been released. Oh and a bunch of those monsters are invincible and can't be killed.
*sigh*
The game does have some cool ideas, like monsters that can only hear, and the weapon crafting system looks fun, but the moment to moment gameplay seems to be very samey throughout.