If you are finding normal challenging then you are at the right difficulty. Tactician isn't significantly different except for the fact that mobs get +20% health, more mobs for some encounters, some mobs have "alpha strike" abilities, and some have additional immunities. The ranged mobs' "alpha strikes" can be devastating when they down your mages at the outset of a battle, which tends to happen early game before you've buffed them with gears (especially the first battle outside of the temple).
