If I had a Vita, I'd definitely pick this up. It looks pretty awesome.
How close is this to, say, Monster Hunter?
It's pretty close. Same overall structure. Faster-paced combat, more customization, lighter ambiance.
I was watching a youtube clip and MH is a pretty close resemblance as far as quest organization and execution, but the combat looks way more like a video game than a semi attempt at a simulation. I say that due to the fact that this game knows its a video game and is not shamed to show it with aerial combat and super combos.
I believe that Monster Hunter tries to be a simulation in a fantasy world with the stamina meter and having to cook food and the awkward controls to factor in weight of the weapons.
RO looks more like King of Dragons with Monster Hunter quest structure.