You want to know what cover really freaked the living heck out of young snell?
And just look at it!! You see the members of the JLA physically distorted into freaks!! And then you see them all lying on the floor, with Batman and Superman strongly implying that they're all dead!! What the hell?!?!?
Fortunately, the original cover (and the story) weren't quite so terror-inducing:
Anyway, aliens are trying to take over Happy Harbor, because aliens. They've managed to send the most powerful Justice Leaguers--Superman, J'onn J'onnz and Batman (!)--on a wild goose chase 10,000 years into the future.
So just just leaves the B-Team to investigate the goings-on at the local fun-house. After they escape an inescapable death trap...
At that point, Aquaman finally shows up, and realizes that--joy!--he's no longer the most useless JLAer!
From Justice League Of America #7 (1961). It was turned into the most terrifying cover ever for Justice League Of America #76 (1969)