I presume you are talking about the european eshop, since only that one has game, and not prepaid cards
I've played almost the whole fire emblem awakening, and it's more than awesome.
Luigi's mansion 2 is a fun game. Not as good as the first one, my first game ever actually, but still, pretty fun.
My bro, who played Pokemon mystery dungeon liked it, not really the kind of pokemon i ever liked thought, the dungeon series.
I hear see very good comments on both animal crossing and monster hunter, but never payed them my self.
As for castlevania, donkey kong and lego city, i have no idea, sorry.
I recommend fire emblem, if you are into strategy. Animal crossing seams very fun, and i;ve been thinking about buying it.
Hope i helped.