At low speeds you're basically driving an electric car that stores the electricity as gasoline instead of in batteries. They get all the electric motor torque and such that you'd expect. Range is between 550-750 miles [3] on a tank of regular 87 unleaded and costs under $30k.
If the ratio of gas tank to batteries were reversed we'd claim it was an electric car with a range extending ICE.
1 - http://www.thetruthaboutcars.com/2014/02/review-2014-honda-a...
2 - https://www.caranddriver.com/reviews/2018-honda-accord-hybri...
3 - https://www.boston.com/cars/cars/2017/04/05/2017-honda-accor...
https://www.pcmag.com/article2/0,2817,2403481,00.asp
This type of products is always higher cost, higher maintenance (two different powertrains), and generally the worst of both worlds (small battery and weak ICE).
The future is fully powered EVs. If buses and semis can be that, then certainly passenger vehicles can, too.
The battery is also big enough that you can drive it pure electric for the vast majority of trips, at full highway speeds. Most other plug-in hybrids can't do that, and I agree they suck.
(The Volt's battery is also carefully used only in the middle ~65%, i.e. not charged all the way and not fully discharged. That extends the battery life dramatically. It can get away with that because the battery is much larger than most other plug-in hybrids.)
The transmission consists of one planetary gearset, and two combination motor-generators. The engine is hooked to the planet carrier, the wheels and a larger motor/generator is hooked to the sun gear, and a second motor/generator hooked to the ring gear. When running on the ICE motor, the smaller electric motor acts as a generator. By varying the amount of current going to the larger motor (and/or battery), it effectively changes the gear ratio. When running on battery, the larger motor is used for motion, and is also used for regenerative braking. The smaller motor is then kicked in at a different speed, to start the ICE engine when needed. Of course, the complexity is all in math that drives the software, but there is much less mechanical complexity in that transmission (compared to an automatic, and even to manuals). But the end result is a very smooth acceleration that seamlessly moves between electric and gas as needed (the feeling is pretty close to what you would get if it was all electric).
Ideally, I'd like to see this for nearly all manufacture models -- electrification added to existing lines, instead of whole new designs.