Curiosity is about twice as long and five times as heavy as the Spirit and Opportunity Mars exploration rovers. Compared to those two, it carries over ten times the mass of scientific instruments.
Curiosity is expected to land on Mars at approximately 10:31 p.m. PDT tonight, or 1:31 a.m. EDT tomorrow morning. It will land, if all goes well, in Gale Crater, a far rougher landing site than any previous mission.
To land, the rover won't descend using the airbag landing system as used on the Mars Pathfinder and Mars Exploration missions. It was felt Curiosity was too heavy for that, and a legged lander meant a design that was felt to be problematic. Instead, for the first time, a "sky crane" will be used. Curiosity will be "lowered" to Mars on cables.
The timeframe of the descent has been dubbed "the seven minutes of terror" by NASA. In seven minutes, the rover has to be slowed from 13,200 MPH to zero. Everything has to work perfectly. A video describing that mission segment is embedded.
The Curiosity rover has its own Twitter feed, and is tweeting away updates as it closes in on the Red Planet. It seems to be tweeting confidently. We'll find out tonight how things work out.