Hmmm, I have a few requests. The basics of the riddler are that he is a super-genious who gives out riddles. Lets go with that:
1) Geniouses in real life tend to make good money, have great jobs and are upper class. Riddler Begins should be no exception... no carnival computer programmer/goth/useless eccentric here. Let the man be successful. That means suits.
2) Let Green & Purple go the way of Batman's Blue and Gray. While G&P is fine for the comics, we can do better, more realistic, more practical and more effective costuming for the movie. He has a suit. Let him start out with the Question-mark Cane, the Green Tie, smooth thin shades and a bowler hat. If he has multiple scenes he can graduate to a green suit with black highlights. I don't care how classic it is, you can't convince me that a super-genious can't figure out that Green and Purple don't go together, or that they somehow look good, or... yeah. Don't force stuff like that, let it flow out of the story.
3) A mystery storyline, obviously. It's time... we need to establish that Batman is also the World's greatest detective, and not just a ninja reject.
4) Killing or not? Let it depend on the storyline, without focusing too much on the victims (ala Saw), we shoudl establish that they could have survived if they had solved the riddle. I think Riddler should be a deadly adversary, but never doing the deed himself. It should all be calculations to him, perhaps he even is remorseful of killing, but to make him unwilling to do it would weaken the villain aspect of his character. You'd be foreshadowing a Riddler-Batman team up.