Life After People was first only a special on History Channel that turned out so successful that they turned it into a series.  The original special was extremely entertaining (especially for those with a love for post-Apocalyptic scenery) and the series mimics that almost exactly.

The only issue with the show is that it tends to fall into redundancy extremely easily.  They try to theme shows toward certain things (what happens to the existing human bodies, etc) but it ultimately still ends up covering the deteriorating structures, buildings, statues, etc over and over.  It will cover different cities (Chicago, Atlanta, Hollywood, Boston, London, etc) but with, ultimately, the same end product; buildings slowly crumble, artwork erodes, animals evolve.

Though this format does stay entertaining for a large number of episodes (especially to those with the aforementioned love for post-Apocalypse), it really doesn't have the longevity warranting an ongoing series.  I wouldn't have minded seeing a few specials (ie; Life After People: Atlanta, Life After People: London, etc), I think the shelf life of this show is waning.