We've devoted more space on AllAboutPrius.com to the 2010 Lexus HS250h hybrid than to most other cars. That's because it can be considered a half-brother to the 2010 Toyota Prius: A fancier, pricier, more powerful sedan sibling to the practical, plain-Jane Prius.

Lexus still hasn't released pricing for the HS250h yet, but then it won't reach dealers until late August, according to Lexus executives.

Now we've had the chance to drive the HS (actually, two of them) through the rolling suburban hills of Westchester County, New York. And we're left wondering whether the 2010 Lexus HS250h will appeal to the same people who consider the 2010 Toyota Prius.

Our longest test drive was in a Smoky Granite Mica metallic Premium model with black interior (a silver standard model appears in the photos). The Premium car was also fitted with the Navigation Package (backup camera and plasma cluster air ionizer), and the Park Assist Package (Intuitive Park Assist and Wide-View Front Monitor).

Mileage

The EPA ratings are 35 miles per gallon city / 34 mpg highway, higher than any other Lexus but lower than the 51 mpg city / 48 mpg highway figures returned by the 2010 Toyota Prius. Keep in mind that's a difference of just one gallon of gas every 100 miles.

Our colleague Bengt Halvorson had a first drive of the HS250h in late May, and in mixed traffic at the southern California preview, he got mileage below the EPA ratings. The HS250h gave him 30 mpg in mixed traffic, and as little as 22 mpg on a hillier route.

In "exceptionally gentle, controlled conditions on level roads", Bengt was able to stretch gas mileage to 46 mpg. That's within spitting distance of the 2010 Prius. And we had pretty much the same experience.

We registered 32.9 mpg after a short 10-mile trip and 36.1 mpg after a longer drive cycle with freeway and local roads, much of it hilly.

We drove the car without working to improve our mileage, but other journalists took to a mileage competition set up by Lexus with glee. The winner achieved 46.2. mpg, and two runners-up did better than 40 mpg.

So it's possible to make 40 mpg, if you pay attention. We wonder how many Lexus drivers--or perhaps HS buyers--will do so. The handling certainly doesn't encourage spirited driving, with a heavy road feel and short wheelbase.

And of course the Hybrid Synergy Drive system controls engine speed separately from road speed, so overall, we weren't encouraged to drive it hard. But perhaps that's the point?

Appearance

Lexus has achieved an admirable 0.27 coefficient of drag, which clearly improves mileage at higher speeds. And the 2010 Lexus HS250h has elements of the characteristic Lexus L-Finesse styling language.

But those styling cues are wrapped around a vehicle with entirely different proportions than the LS full-size luxury sedan. It's longer than the ES, but appears dumpier, with noticeable front and rear overhangs.

From a style point of view, we couldn't help wondering to ourselves if the 2010 Lexus HS250h was the product of a one-night stand between a 2009 Lexus ES350 midsize luxury sedan and the 2010 Toyota Prius hybrid.

Driving impressions

The HS shares its 106.3-inch wheelbase and many structural elements with the 2010 Toyota Prius. But it has a larger and more powerful engine--2.4 liters and 147 horsepower, rather than 1.8 liters and 98 hp--and it's a whopping 600 pounds heavier.

Our impression was that the HS stayed in electric mode very, very little--far less than the 2010 Prius. Even when moving off with a gentle foot on the accelerator, the engine almost always switched on in under a minute.

Sitting in the driver's seat, the base of the windshield is so high that the dashboard top curves up to meet it, preventing even taller drivers from seeing the front corners of the car. The Wide-View Front Monitor (see photo) on the navigation screen provides a measure of confidence in tight quarters.

2010 Lexus HS250h - front wide-angle view

2010 Lexus HS250h - front wide-angle view

To our surprise, the HS has a Sixties-style foot-pedal emergency brake. Once underway, we found full acceleration is hardly head-of-the-pack, but the HS keeps up with traffic.

Like the 2010 Toyota Prius, the HS250h has three optional modes selectable by the driver. The "Power Mode" button definitely makes moving off the line more sprightly, at the cost of gas mileage.

The "Eco Mode", on the other hand, brought performance down enough that the car had almost no acceleration left on uphill stretches.

And the EV button offered electric-only power up to just 21 mph, lower than the roughly 30 mph for the Prius, and it switched back to engine power in well under a minute.

The HS is clearly more refined inside than a Prius, with engine shutoff and restart far less noticeable. In many cases we had to check the instruments to work out if the engine was on--which it almost always was.

However, we didn't like the tire roar and thumping ride from the optional 18-inch wheels fitted with the Premium trim level. We had a short drive in a base model with the standard 17-inch wheels, and those seemed less noisy.

Features

The standard model of the HS250h comes with leather-trimmed seats and steering wheel, a moonroof, dual automatic dual-zone climate control, tilt and telescoping steering wheel, an audio system with 10 speakers and a 6-disc CD changer, Bluetooth with audio streaming, XM Satellite radio, Eco and Power Modes, and 17-inch wheels with all-season tires.

The Premium package adds perforated semi-aniline leather-trimmed front seats,memory for the driver's seat, and power front passenger seat with lumbar adjustment, heated and ventilated front seats, power tilt and telescopic steering wheel with memory, rain-sensing wipers, electrochromic side mirrors with memory and automatic tilting in reverse, wood trim, and 18-inch wheels.

Interior

Front seat accommodation was fine for two 6-foot-plus men, although the center console is offset toward the passenger side. This stints on room for the passenger's left knee, which touches the stack. The driver's right knee has a cutout, so no contact there.

The front seats looked and felt really nice, though. Lexus did a lovely job with the 10-way power adjustment in the Premium model, and we settled into either front seat with a pleased smile.

The rear seat doesn't appear spacious, but Lexus has done a lot of work to reduce the depth of the front-seat backrests. They're also quite arched, so in fact there was enough legroom for 6-footers in the rear, despite the front-seat headrest being closer than usual.

The joystick on the console that operates the navigation display interface was well-placed and intuitive to operate. Like all such systems, owners will benefit from a detailed video tutorial on the system's many, many functions.

One headscratcher: We were surprised that the front console drawer is too small to fit an iPhone, or indeed almost any smart phone.

Summary

Setting aside questions about whether the 2010 Lexus HS250h can create a new "luxury hybrid" niche, we will be curious to see how well the car does in the market. Lexus expects to sell 25,000 of them, against 180,000 copies of the newest Prius in its first full year.

That's probably a reasonable goal. We're just kind of wondering: Are there enough of you Prius buyers out there who want added luxury and a sedan body style, but with some of the hybrid feel, to justify losing that 15 miles per gallon?

Let us know what you think about the 2010 Lexus HS250h. Frankly, we're curious.

2010 Lexus HS250h - instruments

2010 Lexus HS250h - instruments

2010 Lexus HS250h - rear

2010 Lexus HS250h - rear

2010 Lexus HS250h - trunk space

2010 Lexus HS250h - trunk space

2010 Lexus HS250h - door badge

2010 Lexus HS250h - door badge