The Path to War DLC is fun and simple. Luckily, it comes in at only 560 MS Points because the DLC is very short. You gain access to two new weapons though, which might make the price worth it for some just for that. The game itself is more of the same, so if you like playing Armageddon, you'll love playing Path to War.
The DLC itself doesn't have much of a story. It shows a little of what is happening in other areas during the battle of the Terra-former, and you do get to see how Darius ended up in the strike force in the very beginning of the game.
I would only give this DLC 3/5 stars though, because it can be completed in just over an hour and besides some new weapons, it offers nothing new to the game. The "story" that this DLC tells wasn't very interesting and doesn't add at all to the overall arc of the game.
However, the DLC offers VERY easy achievements, and will tack on a quick 250 gamerscore to your game.
I recommend this DLC to hardcore Red Faction fans who just want more, and for those who had a completion and want to finish the achievements. For everyone else, I'm sure this will drop in price eventually. Might be good to pick it up at 50% off.