Haha, yeah, I've tried the game today. It was playable. Waited over two hours in line.
Well... basically, what was playable is much of what you see in the trailer. They put you straight into the action and there is no menu. You have 3 party members: Adol, Seinen no ginpatsu (Silver-haired young man) and Kappatsu na musume (Lively girl). .... Damn Falcom, didn't wanna give us names. :( You can see those in the trailer anyways.
Anyway.... it plays exactly like Ys Seven. Attack with circle, hold R and a button to do a special attack, and L for the super special. Dash with X.
I only had 15 minutes so I didn't really read the conversation boxes, unfortunately.
I got to a point where there was something of a huge enemy, but I was too weak to be able to beat it. He killed me. Then I ran away. :P
Basically, the only thing that was new so far is that you could zoom in and out with the touch screen, and open chests by touching them on the screen. I didn't get to anywhere that required the back touchpad.
I heard, however, different music that was not in the trailer, but the earphones were not good enough and too much noise around so I'm not even sure if it was a remade song found in MotS or Dawn. I haven't played Dawn anyways, only MotS.
Well, that's pretty much it. It's basically Ys Seven. On the Vita. Gameplay wise at least. ;)
You'll laugh, you'll cry and you will never want to go to sleep again. --jollzoffire about Dragon Quest VII
The girl pretty much has to be Karna. She's described as 'Lively Girl' which is appropriate for her, her hair and clothing are the same color as Mask of the Sun Karna if not the exact same design (including the blue headband) and there's no other character in IV it could be and no reason to make a new one when Karna was practically made to be an ally.
As for the silver-haired guy, Lemnos is a possibility but he's a pretty minor character in most versions of the story (he has one important role to play, then he drops out of the story completely) and the one exception was made up by Taito to add 'drama' or something as part of its Karna character assassination arc. Still, that kind of thing can change and he's one of the few good options. The other possibility is Duren, who's somewhat more important for semi-spoilery reasons that I won't mention in case Falcom decides to incorporate it into this game. Granted, that was Dawn of Ys rather than MotS but Falcom could still use it; it's hard to know exactly where the line is between Hudson making things up (blatant stuff like the Black Pearl/Dark Fact stuff) and doing things that were probably in Falcom's plot outline which Tokinhouse didn't use (the names of the five disciples).
To be fair, Lemnos has never been shown as a particularly burly guy either and neither had silver hair in any version of Ys IV so it those respects they're both equally (un)likely to be the mystery man.