I like it. Momentum is very interesting. I like the idea of "spending" your Initiative score for bonuses. Given the nature of what the initiative score means, extra move actions would make sense. Perhaps some other speed related bonuses, like making an opponent flatfooted against your attacks for a round, casting a spell as a Move or Swift action...

Regarding Natural Bond: Does the Ranger only get the 1 Domain throughout their career? Are your new domains really powerful enough to even think of comparing to an animal companion? Could the ranger gain new domains, or have them improved, like how he can get a better animal companion and how they improve? Assuming you're keeping domains at least roughly what they are in 3.5, Rangers will only be able to use up to lv 4 spells anyways. Seems like a very foolish choice to take over an AC right now.

Minor question: Why is your medium save progression +8 at level 19? Wouldn't the pattern dictate it to change from 8 to 9 at 19th level? And that way poor saves "max" at 18th level, medium saves at 19th level, and good saves at 20th level.

Other that that, the class looks great! I can't wait to see the rest of d20r!