Short, boring, and uninspired, Path to War is not worth playing by any means.
Cons: Bland level design; Low production values; Mostly boring vehicle sections; Less than a half-hour of good content
Red Faction Armageddon was a pleasant surprise for me. Whereas most people criticized it for its bland, confined levels (not unfairly), I found that the sheer joy of destruction overshadowed its flaws enough to have fun. For all its flaws, I can easily justify Red Faction Armageddon's existence as a simple fun product, if absolutely nothing else.
The existence of its Path to War DLC can't be justified, however.
Path to War is best described as a haphazard collection of missions taking place around the plot of Red Faction Armageddon. There are cutscenes in each level to tell some kind of plot, but each level is over quickly, the cutscenes are crappy, and there is very little connection from level to level. The developers might as well have not even bothered with the cutscenes, given that they don't make the experience at all more cohesive.
That effort should have probably been put to combat design instead. Levels here are just as bland as in the main game. Except, whereas Red Faction Armageddon gave you fun tools to wreak havoc, Path to War sticks you in vehicles most of the time. And even when you aren't stuck using the uninspired vehicles, you don't get access to any of the fun weapons until the last couple of objectives (which are consequently the most fun).
And then it's over. After only two hours the DLC is over. Now, I'm not of the belief that all DLC has to be Ballad of Gay Tony or Dragonborn length epics, but if you're going to release something that's only two hours long, there should be no filler. Path to War is all filler. At only two hours long, it still wastes your time. For the sake of not wasting your time, if you got Path to War as part of say, a Humble Bundle, I still wouldn't recommend installing it. And I certainly wouldn't recommend buying it.