LotRO player's guide to WoW: General gameplay and combat
As a LotRO player, you may be used to terms like "losing Morale" or "defeated" instead of just plain dying or dead. LotRO's hit point system is based on character enthusiasm during battle, with many classes working towards boosting Morale (Minstrels, Lore-masters, Captains, Rune-keepers) through songs, chants, shouts or other non-magical means. According to Tolkien lore, there's no real way to wave your hand and close up a gaping axe wound, unless you're an Istari. Plus, the simple blanket use of Power for all your skill usage acts in the true sense of the word. It's more a measure of your energy, than anything else, and all classes use it.
In WoW however, this gets a bit more complicated. Players can bleed and players can die. When they do, they are teleported to a resurrection shrine in one form or another. LotRO's version of a rez shrine is called a Rally Circle, where players go to regroup after their failure in battle. Even when a player in LotRO is "defeated", they simply drop to their knees as if fatigued, instead of laying in a heap on the ground. In WoW, not only will you need to direct your soul back to your body for resurrection, but you'll often find the bodies (and eventually skeletons) of previously fallen players scattered throughout the countryside.
WoW also uses much more than simple Power for their skill usage. There's Energy, Mana, Adrenaline, Rage and Runic Power to contend with, all depending on your class and the current state of your class. This adds some complication to inventory management, but other than that is pretty easy to learn.
As we can't seem to mention enough, most of LotRO's game design choices and differences stem from the restriction of Tolkien Lore. Another example of this is no poison usage by "good" players. There are other ways of getting around this, such as slowing skills with the use of tar, for example, but poison is seen as strictly evil in Tolkien's eyes.