Len is a dynamic character who survived abuse and pulled together a crime family (the rouges), only to allow himself to be held hostage to protect his sister's life and then later go out of his way to warn Flash about a plot against his life. Also, he rescued the meta-humans from the Flash before he could lock them up in the Arrow's prison, which was both the opportunistic and heroic thing to do. So, he's definitely not all bad, but he's also got a lot of baggage he's got to work through before he can allow himself to be the good guy he might be. That said, every brush with the Flash seems to bring him closer and closer to the light.
I think he'd be an excellent hero for the same reasons he makes an excellent villain. He's quirky and clever and so dramatic, which makes him so much fun to watch opposite Flash and Mick Rory; plus everyone loves a redemption story. Either way, I'm excited to see how he develops.