Right, the main symptoms of nicotine withdrawal are nervousness and anxiety. I've also been addicted to diazepam, and that was similar, but more intense. I gather that symptoms of opiate withdrawal can be extremely unpleasant. I've had a few small tastes of that, after overusing oxycodone (and diazepam) for back pain. I'd never want to experience the real thing.

I've also done lots of amphetamines and cocaine, and never felt like I was getting addicted. Maybe there's a genetic component.