In its first three months on the market, the Hyundai Sonata Hybrid has established itself as the second best selling gas-electric in the United States, trailing only the indomitable Toyota Prius in sales this summer. But according to a recent Consumer Reports review, the Sonata Hybrid comes up short in several areas, with the publication recommending that consumers steer clear of the model in favor of the gas-only Sonata.

“The Sonata Hybrid is a disappointment, but it’s also an exception,” said Consumer Reports’ Rick Paul to ABC News. “Overall, we’ve seen real improvement with new Hyundais. They generally perform well and provide good value for the money.” So what did the publication find wrong with the Sonata Hybrid?

One of the main complaints was that the car doesn’t provide a smooth transition between gas and electric drive. Unlike many other hybrids with continuously variable transmissions (CVT), the Sonata sports a six-speed automatic, with its lithium-ion-powered electric power taking the place of a torque converter in the powertrain. This configuration allows Hyundai to cut costs and emphasize highway fuel economy where most hybrids perform better in the city. Some reviewers have even noted that the Sonata hybrid is more fun to drive than it’s CVT-driven competitors, but apparently its not for everyone.

Consumer Reports also found fault with the Sonata’s low-rolling resistance tires, which it says diminish the car’s handling and increase its breaking distance. The standard Sonata—which comes without low-rolling resistance tires—gets 24 mpg in the city and 35 mpg on the highway, for a combined rating of 28 mpg under the EPA test cycle. According to Consumer Reports’ own fuel economy tests, the overall rating that car comes in slightly lower at 27 mpg.

For the Sonata Hybrid, the gap between the EPA and Consumer Reports fuel economy measures was significantly greater. Where the car is officially rated at 35 mpg city, 40 mpg highway and 37 mpg combined, Consumer Reports testers pegged the car at a combined 33 mpg rating—6 mpg higher than the gas-only Sonata. That result doesn’t call into question the accuracy of the EPA number (the test cycle also netted a 44 mpg rating for the Toyota Prius—6 mpg less than the official rating,) rather it reflects a different expectation for how the car will actually be driven.

Whether you trust the EPA or Consumer Reports’ numbers, the Hyundai Sonata Hybrid does represent a substantial efficiency improvement over its gas-only counterpart, and fans of the Sonata’s critically-acclaimed interior (particularly those who do a lot of highway driving,) should appreciate the offering—even if it does lurch a little as the gas engine gives way to the motor.

Hyundai can soon expect some stiff competition in the mid-size family hybrid sedan market, as Toyota prepares to release the redesigned 2012 Camry Hybrid this December. The new gas-electric Camry is expected to receive a 43/39 mpg EPA fuel economy rating, with an MSRP nearly identical to the Sonata Hybrid.