I vote for a big picture on the cover, not in a frame, no side panel, only a cool picture on the cover. And if you ask me, I would go for picturing the same group of characters in all the books but in different situations like in RM2 books: fight scene for Arms Law, Using spells for Spell law and so on... but different characters and new style.
And to stand out of all other millions of fantasy rpg covers, avoid overused backgrounds like, dungeons, generic forests... I would suggest:
- Arms Law: Fighting scene in Snow scenary (next to a frozen lake perhaps?)
- Character Law: Huge landscape with our group of heroes in the lower right corner of the picture in small size staring to the horizon and very small because of the distance, just like silouettes.
- Spell Law: A spell user using some utility spell to save life after being thrown from a flaying ship so save his life
- Creatures & Treasures: Creatures! and... Treasures!
Well, I am not to original, but I had to try