Apple's new iPhone 4S, which will hit retailer shelves on Friday, is getting rave reviews from journalists giving it an early spin. (Look for CNET's more in-depth review of the iPhone 4S later this week.)

AllThingsD's Walt Mossberg evaluated the iPhone 4S for about a week and said while the phone looks much like its predecessor, "Inside its familiar-looking body there lurks a nascent artificial-intelligence system that has to be tried to be believed."

The new feature that impressed Mossberg the most was Siri, Apple's new voice-controlled artificial-intelligence system.

"My advice is that owners of theiPhone 4 needn't rush to upgrade; they can get the new operating system," he said. "But owners of older iPhone models, or those with basic phones, will find this latest iPhone a pleasure and a good value."

USA Today was also impressed and agreed that there was probably no rush for many consumers:

"Does that mean everyone who owns an iPhone ought to upgrade immediately? It does not."

"Yes, the 4S has a superior camera compared with the iPhone 4. And it has a clever and obedient virtual personal assistant named Siri who can frequently detect what you are telling it to do and respond in kind. For example, tell Siri you need to wake up at 7 a.m., and the alarm clock on the iPhone 4S is automatically set.

"But most other noticeable enhancements arrive starting Wednesday as part of free software upgrades available to owners of the iPhone 3GS and iPhone 4 (not to mention the iPad, iPad 2 and recent vintage iPod Touch models).

The Verge's Joshua Topolsky agreed:

"This is the easy part... kind of. If you're an owner of an older iPhone, or someone looking to switch to an iPhone from a different platform, there's never been a better Apple device to buy. The iPhone 4S is an astoundingly good phone. Between the hardware (both inside and out) and the software (iOS 5 as well as third party offerings), it's just kind of an awesome package. The lack of LTE, a larger display, or a new design may put off some buyers, but that won't change the fact that 4S is a force to be reckoned with."

TechCrunch's MG Siegler noted that looks and names could be deceiving:

"While it does look the same as the iPhone 4, the 4S contains innards that are a significant upgrade over the previous model. The two biggest changes are the faster chip--the A5 over the A4--and the much-improved camera. Combine those with the new iOS 5 software, and you have what will definitely be a worthwhile upgrade for many users."

Bloomberg was impressed enough to suggest it could have been called iPhone 5:

"In a week of using the 4S, I found so many new things under the hood that, with a few cosmetic changes, the company could legitimately have called it 'iPhone 5' and no one would have blinked."

The New York Times ' David Pogue agreed that those disappointed in the name wouldn't be disappointed in the phone:

"The question isn't what's in a name--it's what's in a phone. And the answer is: 'A lot of amazing technology. And some of it feels like magic.'"

Slashgear said it wasn't just the phone that was impressive, but the entire package created by the new OS:

"There will undoubtedly be smartphones with faster processors, or more megapixels to their cameras, or high-speed 4G connectivity, or bigger, better resolution displays, but it's difficult to imagine any of them competing with the joined-up ecosystem Apple now offers. Challenging the iPhone isn't just about creating one single, better smartphone, but a portfolio of consistent products and services. The iPhone 4S may look the same as before, but it arguably represents just as much of a shift in the industry as the original iPhone ever did."