The first map is like the Roy DLC map. Fight against old FE characters (although these are mostly from Japan-only games) and get one old character at the end, this time it's Leif as a brown haired Trickster, but this time the map is actually new, and large, with higher level enemies and more of them. The interesting bit here, and the reason you might want to buy the pack, are the later two maps.
The second one has the player fighting against all characters from Marth's games (Shadow Dragon and the Japan-only New Mystery), alongside Gaiden characters (also Japan-only) and gets you Alm, who comes alongside a new class (called "Demon Fighter" originally), able to wield swords, axes and tomes, and with two new skills, of course. After finishing the chapter, the player gets an item that can be used to promote any male character to that class.
And the third one has Seliph and the "Paragon" skill, which gives twice as much experience to the unit equipped with it, as well as almost twice as many enemies as the past maps.
