But the laboratory is too big and heavy to employ the bouncing cocoon of airbags that cushioned the landings of Spirit and Opportunity. Instead, engineers devised a completely new landing scheme. After parachutes slow the spacecraft’s descent through the atmosphere, rocket thrusters are to fire, enabling the craft to slow to a stop and hover in midair. The rover would then be lowered via a winch to the surface. (The hovering part of the spacecraft would fly away and crash.)

I hadn't heard this detail before. This seems pretty ambitious. And it's powered by RTGs so it could leave radioactive mess if it crashes.

New Cost Overrun Bedevils Planned Mission to Mars - NYTimes.com