Official Errata

Lightning Strike should say "This damage ignores" instead of "This attack ignores. Lightning Strike is not an Attack event.

Lightning Strike might be the worst card in Thor's deck. It's horrifyingly inefficient if you aren't engaged with any minions (less than one damage per card/resource, ew), and not especially efficient with one engaged minion (if you can manage to pay 4, it's 8 damage for 5+card, which still isn't very good). It only starts becoming efficient if you can wrangle two or more minions: with two minions and 3, you get 9 damage for 4+card, which is respectable. But how often do you get two minions engaged with Thor? Probably not often, even with Defender of the Nine Realms, Get Over Here!, and Angela fetching more. Probably best in Aggression, where you can try to set up a The Bifrost -> Angela play on a turn when you happen to have another minion already. Or in Protection, where you could plausibly tank a small minion for a turn or two until you line up a Lightning Strike and an additional minion.

One upside is that this is not an attack, so you can still deploy it when you're Stunned or otherwise incapacitated. And some scenarios will throw extra minions at you more frequently, which will simplify the process of getting value out of Lightning Strike.