ok, just finished the game. I want to get the platinum but that mastering every skill with every character (and I only used Adol 90% of the time) makes me sad.
anyway, Ys IV, yes, it's really good. (minor spoilers ahead)
I played my first run on normal and the game has been too easy compared to other games like Ys III or Origin. I know that in this one you can use items while fighting but even without that I still think it'd be easier.
story-wise it's ok, some scenes were kind of cheesy and in particular I didn't really like one plot twist but I still enjoyed it. I was expecting more about pretty much everything. for example regarding the whole Darklings thing, the fight of Romun empire, more background story of the most important npcs like Griselda, Leo etc. but I guess some of this stuff will be in other games.
I know that in Ys VI is explained the whole incident between the Eldeen (winged ones) and the Darklings and apparantely that guy metioned by Frieda (his fiancé?) is also the Ys VI villain, I kind of wished they said more about him in this game.
also, the ending. I could say I'm disappointed because I am, since they showed almost nothing but I also understand what they were trying to do with the narrator pov. someone could say it's a "lazy way" to end the game but I didn't dislike it.
now I want to play Ys VI but I'm also tempted to try Ys V with a gamefaqs guide or something like that. from what I read Ys VI is more important and relevant to the "general plot" of the series while Ys V looks like a sort of filler like Ys III, correct me if I'm wrong.