OK, so really quick impressions:
-Looks like Type Moon is sole developer here. I thought that maybe Tamsoft or someone else might be involved, but didn't see any other logos.
-The game is pretty story-heavy and is told visual novel style, complete with different responses you can give. No idea what the hell is happening since I'm not all that familiar with Fate and am general just skipping through it. The cut scenes are both 2D and real-time.
-I love this game's aesthetic. It's bright and colorful with some unique-looking stages (For a musou game, anyway). The character models are pretty cartoony, but that fits in with the general Fate design.
-You can choose between a male or a female character, but this is just for the story; this character is the "Master" and you're playing as the servants in-game.
-The game play is typical musou style- You get two attacks, jump, dash, block, and super move buttons. You can also use different items (abilities?) with the d-pad and can also switch characters. I'm not sure if later levels will allow you to choose the partner, but on the first main level, I was playing as Nero (Saber) and had Archer as my partner. Didn't see anything come up that allowed for any kind of dual attack moves. Not sure if that's in this game or not. Don't remember it from previews.
-The PS4 version has a nice, generally smooth framerate that seems to be 60 FPS. Drops just a bit here and there, at least from the intro and first stages. There's TONS of enemies on-screen to beat up. More than a lot of other musou games, although most are all the same enemy model.
-The Vita version appears to be running at less than half the framerate of the PS4 version. I'd say maybe around 25 FPS? But before you decide to drop this version, it plays smoothly and seemed pretty stable from what I tried. I need to play more of this version though. There's also far, far less enemies on-screen and the resolution and effects are noticeably low-res. If you're only going to get one version, definitely get this on PS4, but the Vita version doesn't seem too bad-it's on par with say, Samurai Warriors 4 on Vita, but retains more details on the characters and levels. I'm not sure if it's PSTV compatible, but it would probably look pretty ugly on the big screen.
Should you import this? I'd definitely recommend holding off for the English release given the large amount of focus on the story.