Land was a criticism of corporations and the wealth driven aspects of society. As most of his movies, it's satire. NOTLD was racism, DOTD was consumerism, DOTD was the military industrial complex, this was corporationism (I guess that is the word).
Fiddler's Green was essentially money in exchange for safety. They made the rest live a relatively fuedal life in exchange they protected them from the zombie hoard.
Often his movies showcase man's shortsightedness and inability to coroporate and work out solutions. This is no different. It also was a homage to the past movies. The constant references to Canada, Tom Savini's Biker Zombie, a few lines which made reference to previous films were all put in.
No, it is not the strongest of the series, but it's still damn good if you can appretiate Romero's vision.