At $6.99 on Steam, you're getting plenty of game. The campaign is challenging (if a bit brief). This DLC also introduces cargo space in vehicles, which carries over to the original game and the Breakdown DLC as well. You don't need to buy Lifeline to get that particular benefit, but it was introduced with the expansion.
This DLC adds to the overall value of the original game, which is currently priced at $19.99 on Steam. For about 35 bucks, you get the original game and both DLC expansions, which provides more total gaming hours than a lot of $60 "triple-A" titles.
The campaign is fairly short, but you can play it over and over and get a different experience each time because of the random nature of the quests. You really never can tell when a random Feral is going to completely alter the course of your game.
I had a really spectacular Feral-failure: I had rescued a story-important NPC from a building and everything went fairly smoothly. We had gathered everything we needed and were getting ready to leave when I got a notification about something. I don't remember what the notification was, but it caused me to pause to check my map when we got out into the street. I closed the map just in time to see the Feral - which had likely spawned in the Danger Zone, behind a tall wall just a few feet from where we were standing - pounce upon my partner and rip her in half.
Luckily, we didn't need her - we just needed her lab notes. And zeds don't eat lab notes.
That's exactly the sort of thing that makes each play-through unique, and that uniqueness makes you want to play it again after you've beaten it the first time.
A worthy addition to the State of Decay universe and the zombie-survival genre in general. If you are a fan of the original game and want to see what kind of shenanigans the army gets up to, it's absolutely worth checking out.