User blog comment:Wildcowboy/RDR game of the year review/@comment-2113545-20111129024330/@comment-1265875-20111129165907

* Maximum health is reduced by half. * Health regenerates more slowly and begins refilling after a longer delay. * Dead-eye does not automatically fill over time. It must be earned by killing enemies or using items. * Horses do not regenerate. If killed, you must purchase, steal, mount, or break another horse and then hitch it to a post to earn the right to call it by whistling. Note that horse deeds are still available and unlimited, but twice as expensive. * Store items cost more. Sell values are lowered. * Reward/drops/looting amounts are lowered (ammunition and money). * Pardon letters are more rare. * Fame and Honor gains are reduced. * Mini-game buy-ins are lowered to match the scarcity of money. * Warhorse deed must be purchased for $10,000 (available in any General Store). * Deadly Assassin outfit increases the amount of Deadeye gained from kills, rather than over-time regeneration. * Note that Hardcore is only available in the normal Red Dead Redemption campaign -- Undead Nightmare is unaffected.
 * Aiming is permanently set to Expert.

Other Tips

* As with the original Single Player campaign, health regeneration in cover is higher than out of cover. Use this to your advantage! * Master Treasure Hunter increases the maximum stack size for all items from 5 to 10. You can now carry twice as many dead eye items at once. * Master Survivalist allows you to loot an additional type of dead eye regeneration item from plants, increasing the number of dead eye items you can carry.

Hope that helps! :)