This is really risky and nowhere near as much of a "sure thing" (inasmuch as such a thing can be when we're talking about enterprises like this) as any previous successful landing.
Essentially, tonight (at least for US values of "tonight") we are using a sky crane to land a robot car on Mars - this is way better than measuring how many kilograms a genetic freak can lift over his head. Proof that we [1] can still build great big awesome things when we decide we want to.
[1]: Mankind, not the US. This should not be a nationalist moment.