Fire Emblem Awakening [SPOILERS INSIDE]

Lunatic + is supposedly twice as hard. They get skills such as Luna (halves def/resist) as soon as the game starts. You essentially pray to the RNG god's the entire time.

It's actually worse than that. Enemies have "+" versions of certain skills. For example Luna+ gives every attack the Luna effect. Apparently some enemies also have a skill called Hawkeye which gives them 100% accuracy on every attack.