I just finished it. Getting a handle on blade mode was interesting, and it was weird not stealthing around in a Metal Gear game. With that said, I enjoyed it for the most part, could not stand Jack's voice... like sandpaper on nipples kind of irritation.
It was fun chopping stuff up, and I freely admit, I let out a little fangirl squeal when my favorite side character appeared.
I'd give it a 4 out of 5. It definitely added to the Metal Gear lore, and has me stupidly excited for Ground Zeroes.