What you get out of the card is pretty solid. For 2 resources you are dealing 3 damage and preventing 3 damage.
In comparison, you could have both Haymaker and Expert Defense in your deck to accomplish a similar goal with two cards and the same resource cost. However, the two cards just mentioned take care of burst damage which maybe more important based on your situation than the value you get out of Energy Barrier over time.
You can at your own leisure reduce some incoming damage when it comes your way. But, you can't deflect all 3 damage at once that is coming at you. It triggers off of any amount of damage to prevent and reflect 1. You can't take 3 damage and remove all three charges to prevent it all.
But it is still a solid card that for the most part should be used up when you know some incoming damage is coming your way or better yet when you can use it to your advantage in the follow up turn after getting attacked. If a minion on you has 3 health remaining and you use one charge on this to prevent the damage he dealt and bring him down to 2 health, your ally or hero might now be able to finish him off without having to dedicate something else that turn.
And of course, it gives protection a solid fighting chance against encounters similar to Ultron's Ultron Drones. A couple of these on the table can satisfy a similar condition that you would have if you were to play leadership with Hawkeye. They can really put in some work.