The GM Voltec drivetrain was technically excellent, but they put it in the wrong vehicle. Small sedans (or pseudo hatchbacks) like the Volt are a dying market niche. The interior was cramped, especially the back seat. If GM had put the same drivetrain into a compact crossover SUV with a little more interior comfort and cargo space then it would have been more successful. Look how popular the Toyota RAV4 Prime plug-in hybrid SUV is.