Obviously, the entry, decent and landing is a very big challenge. I think we're going down the path...retiring a lot of the risk in the technology. But there's still the whole validation process...and still a lot of effort ahead to make that work.
We're going to be able to learn much more from orbit. And I'm confident that in the end we'll pick out the best MSL landing site. If you only have one to send, you send it to the best place you can on Mars.
Entry, descent and landing are very complex, and a lot of things have to go correctly. That's just part of the risk associated with the mission.