It's an incredibly overcomplicated mash-up of electric and hybrid technology. It's got a low-speed motor, a separate high speed motor, a gas engine that can drive the high speed motor as a generator, and a mechanical connection so the high speed motor/generator drives the wheels directly, i.e., an ordinary car. There's a management system of the complexity you'd expect to run all the gears and clutches to control all this stuff.
GM claims that all this wizardry produces fabulous efficiency, but it tells me that it's a prototype in which nothing works quite as well as it was supposed to. It's also a significant admission of failure, since as recently as June Chevy swore that the Volt would be pure electric, not a mechanical hybrid. This car is basically a Prius with a power cord.
I also think they misread the market. The main competition to the Volt is the pure electric Nissan Leaf at $33K compared to the Volt's $41K, both before $7.5K tax credit, and the Prius at $24K to $32K depending on model. The Volt can go about 40 mi on battery, then another 300 on a 9 gallon tank of gas, they claim 50 mpg, but 300/9 is an unspectacular 33 mpg.
The Leaf can go about 100 mi on a charge. The Prius gets 50 mpg, and Toyota says that in 2012 there will be a plug in version that can go 13 mi on a charge before the engine kicks in. (Their battery is smaller and lighter, improving gas milage.) The Volt is all-American, loaded to the gills with bells and whistles like a 30GB disk to store the music you listen to through the Bluetooth link.
Given how exotic the Volt is, it doesn't strike me as anyone's only car. People will be buying it because it's cool, particularly once they discover the stupendous startup acceleration that electric motors provide. That means the range boost from the gas motor is not as important as for a normal car. The Leaf, by comparison, is squarely aimed at trendy greens. All the plastic is recycled, and they even offer an almost entirely decorative solar panel/spoiler.
If they sold Leafs around here, I would consider getting one as a second car. They say the range is about 130 mi under ideal conditions (no heat or A/C, downhill both ways), and 65 mi worst case (stop and go with the heat or A/C blasting.) Most of my trips are down to Ithaca to do errands, about a 20 mile round trip, so it would handle them just fine. It's much simpler than the Volt, and I expect it'll be much more reliable, and get better electric efficiency. Or maybe I'll wait and get a plug in Prius, since 13 mi is most of the way to Ithaca and back, and I have cheap overnight
power, or the Honda Fit EV which looks to be similar to the Leaf.
I expect a second generation Volt with a lot of the crud worked out could be a good car, but not this one.