According to PSM3, the campaign is roughly only 5 hours in length. This of course does not take into account the multiplayer, and leveling up system there, but only the single player. Though rather than knock the game for the length of the title, PSM3 actually said it wasn’t really an issue:

That short, short length of the main story may seem like a major sticking point, but it isn’t as significant as you might fear. Homefront is relentlessly brutal and constantly puts you in new, unusual and memorable scenarios, varying the pace to keep things interesting.

While there may be many who decide not to give this game a try based upon the time length of the single player, who here still plans on getting the game regardless?

[Source]