Ich bin in einen englischen Forum auf eine gute Antwort gestoßen - Google Übersetzer hat sie leider so grauenhaft übersetzt das ich dir den Originaltext schreib ( setz ihn einfach in Google Übersetzer ein - man kann verstehen was gemeint ist ;) )

It depends on the player.

Breakdown is similar to the original game, except the missions are removed and it's just about surviving as long as you can. Build the best team and just survive--go as fast or slow as you want. Outside of new survivors you can play as (including characters you couldn't control in the original), as well as new weapons, the game play itself is very similar to the original with the catch that each new level becomes slightly more difficult (up until 11--after that it stays at the highest difficulty level). There's no end game, you just keep playing forever.

Lifeline is a whole new mission based story--basically the military's story on the other side of the wall as they are trying to figure everything out. There's new elements to the gameplay (being able to give standing orders to the other soldiers, base sieges, new facilities, heliport drops, etc.) There are multiple endings, so it's meant to be replayed a couple times to try for different endings. So it really depends on what you like. I like both. If you enjoyed the original and just want more of the survival aspect, check out Breakdown. If you want a new story/map and a more fast paced version, check out Lifeline.

Quelle: http://www.gamefaqs.com/boards/681534-state-of-decay/69453249