What made it particularly dangerous a few years back was the traffic on that Death Road. I went down there in 2003, and there used to be a lot of trucks going up and down. The road isn't wide enough for two trucks side by side, so it was very hectic.
At that time, a new road to Coroico was being built and I heard it is finished and open to traffic now. Meaning the Death Road should have a lot less traffic on it.
I'd say it's not that dangerous on a bike, provided that you don't let yourself take too much momentum and keep away from the left side with the drop.
I think the scenery makes it worth going there, rather than the thrill. It's absolutely beautiful, and Coroico makes for a nice change if you've spent some time in the Altiplano: it's a lot warmer, the food is better, it's very relaxed , green and lush.