If any classical symphony is memorable as a whole, it's probably Beethoven's 5th too, and I'd wager that people not being intimately famililar with it is mostly because they've never consciously listened to the symphony as a whole. It's an extremely catchy symphony because each of its movements essentially just is very cyclical and built from a few central themes, with no meandering or useless notes at all, and just enough variation to keep it fresh but not enough to break the repetition that makes it catchy.