OMG I GET TO TALK ABOUT YS
Interestingly enough, Memories of Celceta has a bit of a different gameplay system than most of the other Ys games--the only other game that has a system like it is the PSP exclusive Ys Seven (by which I mean the whole party members thing). I honestly haven't looked into this game too much, since I don't have a Vita, but I can tell you that it's a remake of Ys IV, which had never released outside Japan until this release. Also, this is the first version developed by Falcom themselves (the original two versions of Ys IV were outsourced to other companies), so fans of the plot can finally get a completely canonical Celceta story.
As for the series in itself, most of the games are really fastpaced and can be quite difficult, but the new party member system and whatnot kind of help to make things easier. While all of the games have a connected plot, you really can jump in at any game but Ys II and still be fine--you'll just miss a couple minor references and maybe be slightly confused as to why some weirdo named Dogi is following you around. If you end up enjoying Memories of Celeta, I highly recommend you try Ys Seven, and then the rest of the series from there. Oath in Felghana is personally my favorite (remake of Ys III), but it's not good to spoil yourself on the best first ;D