The cards are cryptic for a good reason: you're supposed to experiment with them to understand their effects. The problem comes when you've seen them all, and can't remember exactly what Justice, or the Joker, or the individual runes do.

Every card now has an appropriate description for its effect -- every card has been updated this way.

Pills don't have descriptions, but Bad Trip and Health Down carry asterisks, to denote their special behavior when at low health. Pheromones also denotes "Charm", mostly just because I can never remember the effect.

Goes well with my improved item descriptions mod: http://moddingofisaac.com/mod/158/improveditemdescriptions

Inspiration came from the Clearer Items Description mod by BlueSpike: http://moddingofisaac.com/mod/41/cleareritemsdescription
Big thanks to the http://platinumgod.co.uk/rebirth site for making checking everything so simple.