His new armor is no longer a bulky unit which houses its own AI "response server" and miscellaneous interfaces for neural control. Instead, it is more lightweight (constructed of a pliable crystalline material with a molecular structure that can collimate into super-hard planes upon the application of an electrical field) and less complex (as it interfaces directly to Stark's brain via the Extremis-modified cybernetic connections), and has much faster response time since it effectively functions like Stark's second skin.
He is also able to remotely connect to external communications systems such as satellites, cellular phones, and computers through the PAN interconnect (that is now thought-controlled). Because the armor's operating system is now directly connected to Stark's nervous system, its response time has been significantly improved.
Another major departure from the previous armors is expansion of repulsor technology. The "repulsor flight system" provides lift (something like anti-gravity) and positive flight control (pitch, roll and yaw), while the usual rocket boots provide the armor with thrust. The same repulsor technology allows the individual pieces of the armor to levitate and assemble themselves, by modulating what Stark referred to as "vectored Repulsor fields".
Furthermore, the Extremis process has endowed Stark with a 'healing factor' and possibly even enhanced physical abilities, as he was confident enough to challenge Logan/Wolverine to a fight (and even challenging to see who's capable of recovering faster from the other's attack). It was later stated that the Extremis enhancement speeds up a person's repair process and hence the body's cells died and regenerated at a faster rate. This effectively made Tony Stark immune to cancer and gave him his 'healing factor'.
In the Iron Man: The Inevitable storyline, it was shown that it's not only Tony Stark's body and the interfacing undersheath that has self-healing properties. Even the Iron Man armor has the ability to self-heal and self-repair, presumably through the use of nanotechnology. The armor is also able to store power throughout its structure, indicating that instead of having main batteries mounted around the waist as in the older Iron Man armors, the Extremis armor incorporates distributed and decentralized energy storage.
Note: Although Extremis for reasons of simplicity is referred to as "a virus", it is not. The Extremis process involved injecting several billion microscopic nanotubes, which act as information carriers, into the brain. The brain is then partly reprogrammed; the so-called "repair center," that part of the brain which maintains an "integrity map" of the body, is told that the body is wrong. The physical reaction is that the entire body regrows itself, remaking itself per the Extremis instructions. Extremis itself, the original information package, is not involved; neither are "nanobots."
After the entire Stark 'dataspine', the central data processing center which governed all, or at least the pertinent portion of Stark technology, was infected with a hyper-advanced, Skrull-developed computer virus during the "Secret Invasion" storyline, Tony lost the ability to use Extremis' interface functions and consequently the armor was rendered obsolete. For the 2008 "World's Most Wanted" storyline, Tony used older armors, such as the Heroes Return and Classic Red and Gold versions.
