The next step up is the value leader, the 2.5S with the same engine and a sticker of $20,425. It comes with disc brakes, halogen headlights, a six-speaker stereo, power windows and locks, air-conditioning and six air bags. It even has an “intelligent key” that needs only to be near the car to unlock the doors and enable the starter.  But the great majority of Altimas delivered will come with some of the many available options. First on the list is a continuously variable transmission, or C.V.T., the only automatic available on Altimas ($500). Antilock brakes ($300), a rear spoiler ($360), an electrochromic self-dimming rearview mirror ($280) and fog lamps ($310) can also be had à la carte.  But most options for the 2.5S are delivered in bundles. To get the satellite radio you must buy the premium Bose sound system ($1,200). Opting for a navigation system along with the Bose means buying a rearview camera and a Bluetooth phone system ($3,200). To get leather, you must buy a power driver’s seat, power sunroof, alloy wheels, heated front seats, automatic dual-zone air-conditioning ($3,850). So an Altima 2.5S configured just so can get expensive, fast.  The Altima’s other trim lines are built around Nissan’s mainstay VQ35 engine, a 3.5-liter aluminum-block V-6 that also powers the Maxima sedan, Quest minivan, Murano crossover and 350Z sports car along with the Infiniti G35 and M35. The Altima’s version of the engine yields 270 horsepower and 258 pound-feet of torque.  The Altima 3.5SE, with a power driver’s seat, C.V.T., 17-inch alloy wheels, antilock brakes, fog lights and a better-looking interior than the one in base 4-cylinder cars, costs $25,125. The plusher 3.5SL ($29,015) comes with all the expected goodies: leather, sunroof, automatic climate control, premium sound, xenon headlamps. Those who truly aspire to luxury can spend $2,000 more on a navigation unit, rearview camera and satellite radio (with perhaps the industry’s most maddening satellite radio interface).  I drove the 2.5S, 3.5SL and the first-ever Altima Hybrid on the hilly open roads around Santa Barbara, as well as on the mean freeways of Los Angeles, and I was impressed by what a good car Nissan’s midsize sedan has become. Start with the 2.5S, which Nissan expects to constitute more than half of Altima sales.  The interior, which in previous incarnations was dulled by acres of economy-grade plastic, is still unlikely to be confused with the cabin of an Audi or a Lexus, but it is now pleasant and airy. The gauges and controls are nicely positioned and the buttons are big. The front seats, built for well-fed Americans, are comfortable, if less supportive than I would have liked on twisty roads.  The rear seat, usually an afterthought in midprice sedans, is first-rate.  (One glitch has recently surfaced: if the remote keyfob comes in contact with a cellphone, under some circumstances the fob’s coding is wiped out and it becomes useless. Nissan is working on a fix.)  The real payoff to the redesign comes in the driving experience. A stiffer body and reworked suspension make the Altima a pleasure on curvy roads. In its class, only the shorter-wheelbase Mazda 6 is more fun to drive. And the new Altima 2.5S is considerably quieter than the old one: the engine barely purrs at cruising speed. In fact, the in-line 4 could be mistaken for a V-6 until you floor the accelerator and the valves begin to clatter.  What most distinguishes the Altima, though, is the C.V.T. One way manufacturers have improved the smoothness and efficiency of automatics is by increasing the gear steps (to five, six or seven); the Lexus LS 460 has eight. The C.V.T., in contrast, uses a system of belts to change gear ratios continuously from very low to very high.  This is hardly the first such transmission on a passenger car, but it is surely the best. Larry Dominique, vice president for product planning and strategy at Nissan North America, noted that previous C.V.T.’s were smooth but had a rubber-band feel because the engine speed seemed unrelated to throttle pressure.  The far more sophisticated programming in Nissan’s new version delivers a more natural experience. Downshifts are almost instantaneous yet perfectly smooth, and Mr. Dominque says mileage is as much as 10 percent higher. Indeed, this C.V.T. is so clever that in auto-manual mode it simulates six discrete gears quite well, giving hands-on drivers intuitive, responsive control.  With an extra 95 horsepower and 78 pound-feet of torque available, the Altima 3.5SE is more powerful and even quieter than the 2.5S, as well as more luxurious. According to Car and Driver magazine, the Altima accelerates from 0 to 60 in just 5.9 seconds with a manual transmission — quite zippy for a car in this class. From my own experience passing trucks on hilly roads, I can testify that the C.V.T. delivers torque when you need it.  The modest downside to all that power is a bit of torque steer — a distressing, though generally harmless, tendency of powerful front-drive cars to hop in your hands at full throttle. The bigger engine also adds almost 200 pounds to the weight, which slightly degrades cornering.  Not surprisingly, more power also means lower mileage: I managed about 23 m.p.g. in mixed city-highway driving, about 3 m.p.g. less than with the Altima 2.5S.  The Altima may lack the reputation for bulletproof reliability of the Toyota Camry and Honda Accord. It may not handle quite as well as the Mazda 6 and it is certainly more expensive than comparably equipped Hyundai Sonatas, Saturn Auras or Ford Fusions.  But the C.V.T. and the muscular V-6 make the Altima a bit more exciting and versatile than the competition — at least until an all-new Accord comes out this summer. And, for my money, the Altima’s snazzy new shape gives it an edge in styling. Nissan, it seems, has gone back to the old well and found a new supply of driving elixir.
The redesigned Altima gives Nissan a bit of needed sizzle in the crowded market for midsize, midprice front-wheel-drive sedans.