It certainly looks like overly complex. The simplest system, that is, airbags, are unusable because of the size (it's almost like the difference between a big toy car and a regular car)
You probably can't brake it only with retrorockets, and as this mission is aiming to be the most precise landing on Mars ever (and I'm not even sorry for the pun) they need a way to get the lander to an exact location (by deploying it from the crane)
People seem to forget/not realize that the EDL (entry, descent and landing) of Spirit and Opportunity had pretty much all the elements that the Curiosity EDL does PLUS the airbags and the airbag cocoon: http://www.youtube.com/watch?v=Ij33yhdGn_g
Leaving out the sky crane means that the comparison doesn't involve "pretty much all the same elements." The MSL sky crane is insanely complicated. Not much can go wrong with an airbag, relatively speaking.
I'd compare it to Cassini-Huygens, more than Spirit and Opportunity.
"not much can go wrong with an airbag" -- not true. The mission designers for MER (Spirit/Opportunity) admitted that a wrong bounce or an initial collision with a sharp rock could spell doom.
I think the airbag relies considerably more on good luck. You can't really model collisions the way you can a descent on a cable. The latter is 100% engineered.
But as the video shows, the MERs did have a similar system - after the parachute phase, the rover in its cocoon was lowered from the aeroshell at the end of a tether. Then, the retrorockets in the aeroshell fired, bringing the whole thing to a full stop some tens of meters above the ground. After that, the airbags inflated, the tether was severed, and the rover dropped the rest of the way to the surface.
It certainly looks like overly complex. The simplest system, that is, airbags, are unusable because of the size (it's almost like the difference between a big toy car and a regular car)
You probably can't brake it only with retrorockets, and as this mission is aiming to be the most precise landing on Mars ever (and I'm not even sorry for the pun) they need a way to get the lander to an exact location (by deploying it from the crane)