A magic focused pack with a little tech. All world generation replaced by Thaumcraft's Tainted Lands. Combine that with the Meteorcraft mod and Funwayguy's Epic Siege Mod and survival becomes a challenge you may not survive.
There is an in-game guide to help the player along, plus SimpleAchievements provides a set of goals that form the endgame, the way to "win" the pack.
Health regen has been turned off, the gamemode is set to hardcore. To compensate, armor gives you absorption hearts that do regen. You can get up to two extra bars of hearts with good armor and proper enchants. You also start with a Golden Laurel Crown to provide an extra life.
Fastcraft is HIGHLY recommended.
Any issues go here: http://minecraft.curseforge.com/modpacks/229447-atonement-sins-of-the-past/issues