the term "Landbier" describe a traditional type of beer. It is not a typical type of beer, but it is traditionally brewed. The term "Landbier" is rather a term used for advertising :-)
Schlapppeseppel Landbier is a 5.3% yellowish amber coloured lager with almost no head to speak of. It's as cloudy as a heffe though. The aroma is one of straw and orange with orange evident in the flavour as well. There is little in the way of hop character and almost no bitterness either. Instead the caramel malts seem to dominate but not at the level you might get in a Bock.
All in all, it's a nice beer but not something I can see myself drinking.
Since the Landbier I had is pretty much different in every conceivable way to the one TBN had, I can only conclude the Felix is right and Landbier is less a style and more a term used for advertising a traditionally brewed country beer of miscellaneous style.