Rangers are champions of the natural world. They are typically good aligned, and their link to nature gives them supernatural abilities. They are the paladins of the forest.
Really? REALLY? That's the archetype they are going for? Fantasy Greenpeace on steroids? Setting aside the mechanics for a moment, I just don't think they have the feel down. I thought we had left the whole Ranger is to Druid as Paladin is to Cleric forced symmetry behind.
Also, the whole 'spirit companion' thing seems to overlap with the Totem Barbarian a little too much, at least in concept if not mechanical execution.
The Ambuscade ability will be one level dip multi-classing fodder, I thought they were trying to avoid that this addition? Even outside a multi-class it may be too good. Will have to be play tested. I suppose with multi-classing being optional, it is just another good reason to look long and hard before allowing it in your game.
I'm not really all that inspired by the spirit companion thing, like they just phoned it in with the bear, eagle, wolf distinctions. It seems this class would be strong on a smaller number of encounters a day (most classes are, but this one is particularly so), and weaker with more encounters. The fluff and the mechanics just don't really match, or rather just seem kind of arbitrarily paired together.
EDIT: unlike many others, I don't mind the 2d6 hit dice. It could be a nice touch, but I'm not married to the concept.