It's a new direct injection engine GM developed to replace the old pushrod 3.1L in the lineup which will be pumpin out about 220hp. It might end up being another optional engine in the list in the future. They will be using the 3.6L DOHC for the LTZ. Another rumored engine is a DOHC 3.9L for the SS that should be good for just over 300hp.
Another thing of note, Stabilitrac is available on all but the very base models. For $23K you get 4 wheel discs with stability control, power windows/locks/trunk/seats/steering/mirrors, heated seats, steering wheel audio and cruise controls, garage door opener, XM radio, 17" chrome wheels, remote start, Onstar, leather steering wheel and shifter, 8 airbags, acoustic laminated windows, MP3/CD 6 speaker stereo, and a tire pressure monitorng system.
Despite being competition for the Fusion, the size of this car and interior space edges in on the Taurus (500) market as well. Unless people are just unwilling to give GM a chance because of "it's another crappy Chevy" syndrome, I think this car should be a pretty good seller. Only time will tell though. I was dissapointed to see that even though it is a very nice car, and received accolades from the press, the Aura sold about as good as the PS3.