That depends on the type of undead you become
The people of Geb are from a varied type of undead, some are zombie lords, ghouls, others are vampires, there are ghosts (like Geb himself), liches (Arazni). It all depends on how they died/what killed them, and other conditions necessary for each type of undead.
Example, those killed while infected with a ghoul's disease will likely raise as ghouls (or ghast if they have 4+ HD). Those bitten by a vampire might turn into another vampire. Powerful spellcasters who safeguard their soul in a phylactery might return as a lich upon death.
Anyone who dies on Gebbite soil is reanimated as a mindless undead creature to serve the state in eternal bondage. Those with sufficient clout or wealth generally circumvent this procedure, and willingly transform themselves into an intelligent undead creature, either through dark magics, or simply by letting themselves be killed by ghouls, vampires, or other creatures with the ability to create such progeny.
But there are also zombie and skeleton laborers all over the country. Those are clearly mindless and have no memories of their past life.
Geb is now renowned as a land of the undead, and while plantations filled with zombie labourers may stick in the mind, there is much, much more to Geb.
With its ruler now an immortal ghost, and much of the populace animated as skeletons and zombies, the land of Geb became known as a land of undead, much to the dismay of neighbouring and not-so-neighbouring nations.
Keep in mind however, that not everybody in Geb is an undead, only the majority of the population due to the "enviromental curse" on the country. This is specially true about travellers and merchants from nearby countries.