The first time I saw this card, I thought nothing of it. Oh, my past self was so dumb. It's a great way to add extra actions to the board and protect the weakest allies. Not only that, but it is a neutral card that you can use to create some interesting combos.
Need one extra charge on the fate meter but you can't afford to lose an ally? No problem, charge the fate meter with this beauty and you are gold.
A strong villain is causing you trouble but you need two attacks to kill it? Easy, attack with your hero and activate guard. If the villain is about to die from the next hit, he will hesitate because of your guard.
Need some interesting combo ideas? How about Mithril Shirt + Enduring Valor on Tom Took (use his power to ignore two consecutive attacks)? Or Aragorn with Enduring Valor + Sword of Númenor to potentially give you 4 resources in one round? Give Spear of the Citadel + Enduring Valor to Dwalin/Dáin/Gimli for many consecutive guard actions.
Bottom line is: this card seems one-dimensional (to new players) until you start to experiment with it. Go nuts!