FORTUNE — Let’s get this out-of-the-way first: If you were expecting a mind-blowing revamp with the iPhone 4S, you may be disappointed. Everything about its industrial design will be familiar — it sports the same gorilla glass front and back, the same 3.5-inch-sized Retina display and a similar-looking metal band surrounding it.
That’s why some, like The Huffington Post, found the announcement “hugely disappointing.” Where was the larger screen? What about the oft-rumored teardrop design? Where was the iPhone 5? Many of us became so preoccupied with rumors, wishlist features, unfounded mockups and the number attached to the name that they ignored what the 4S was and harped on what it wasn’t.
Part of that may be due to Apple (AAPL) itself. If you haven’t noticed lately, it’s been on a roll. The iPad exploded the virtually nonexistent tablet market, selling 14.7 million units during its first year on the market. Meanwhile, Apple is expected to report record Mac sales. On both fronts, the company has rather aggressively updated, first with the iPad 2 and then with the new 11-inch and 13-inch MacBook Airs. In both areas, the company has innovated far enough ahead that its competition is still trying to catch up. Given all that activity, expectations for the newest iPhone were at an all-time high.
The 4S’s look isn’t a bad thing — it’s just very familiar. And if you’re happy with it, you won’t be alone. The company reported sales of more than 4 million units during the smartphone’s first three days, 135% more than the launch of the iPhone 4 last year. That already flies in the faces of some analysts who predicted users might skip this upgrade and wait until next year. Haters will say the 4S design is more of the same, but let’s face it: there are few smartphones that make a visual statement quite like the iPhone 4’s — and now the iPhone 4S’ — even now.
As earlier reviews suggested, the real changes reside within the 4S’s familiar chassis including a dual-core A5 processor, 8-megapixel camera and 1080p (a.k.a. HD) video recording capability. (Apple loaned us the $399 64 GB iPhone 4S in white.) For our reviewing purposes, we’ll focus on what’s unique to the 4S, and while iOS5 with its updated notifications system and iCloud support mark a major software upgrade, its availability on some older iPhone models means it’ll be less of the focus here.
With that dual core processor — similar to the one in the iPad 2 — you’ll obviously notice a speed increase, more so if you’re upgrading from an older phone like, say, the 3GS. The difference between the two should be night and day. If you’re an iPhone 4 owner, it’s less a jolt and more of a speed bump. Apps generally launch faster and zip along, and more graphics-focused programs like Maps respond instantly as you zoom further in on street blocks. (Games like Infinity Blade 2 will better show off the 4S’ new graphics power in the coming months as they are updated to take advantage of the hardware.) Web pages, overall, load more quickly whether over 3G or WiFi, and there’s little-to-no lag as you tap away on the virtual keyboard.
There’s been a lot of talk about the new 8-megapixel camera, which reportedly captures more light and provides sharper images. It’s even been suggested that it could replace many dedicated point-and-shoot cameras. We wouldn’t go so far as to tell you to put that $250 camera on eBay, but the 4S consistently took brighter, clearer photos in sunlight than any previous iPhone before. Images taken in the evening also turned out better, with sharper definition of objects and overall less graininess, as you can see below. A faster shutter speed with the high dynamic range (HDR) option off makes shooting a breeze. Unfortunately, the front-facing camera doesn’t fare as well: it’s still the same fuzzy, low VGA resolution.
The video camera got a bump, too. Now it captures video in 1080p. Video is every bit as clear as stills, and thanks to image stabilization, I don’t need to carry my Flip Ultra HD around anymore. With iOS5, you finally have more direct access to the camera: double tap the home button when the phone is off, and a camera icon appears. You can also press the volume up button to snap shots.
Depending on which mobile carrier you’re with and where you live, you’ll get different results with call quality and download speeds. In San Francisco, where AT&T is notoriously spotty, the 4S did fine. We didn’t notice a huge improvement in call quality (good, not great), and we still experienced dropped calls. Download speeds fared better. While the 4S isn’t technically a 4G-labeled device, downloads of web sites and apps were generally quicker than the iPhone 4, though not as fast as Verizon’s 4G network in the area.
A Siri-ous voice assistant
Much has already been made of Siri, the voice recognition “intelligent assistant” that’s exclusive to the 4S. It seems one of her (of if you switch to the English UK option, his) best assets is an especially dry sense of humor. Ask Siri to marry you as I did mere hours after receiving the phone to review, and it’ll say that it hardly knows you. Push the subject, and it’ll claim that her “End User Licensing Agreement does not cover marriage.” And if you ask it about one of the 20th century’s biggest mysteries — “how many licks does it take to get to the center of a tootsie pop?” — you’ll get an answer (3,481).
When you’re not kidding around, Siri’s also good at performing some practical tasks. Ask it where the nearest sushi place is, and it’ll present a list of sushi restaurants in descending order based on proximity; ask it which one is the best, and it’ll sort those nearby restaurants by rating. Siri is also handy with basic text message dictation and short emails, though I’ve noticed punctuation isn’t its strong suit. Likewise, scheduling appointments and even avoiding double-bookings, is much easier. I didn’t use the calendar app on the iPhone, but because of Siri, I do now.
But Siri isn’t without its quirks. Apple says the app is still in beta, and our experiences bore that out. Siri sometimes has problems understanding what I’m saying, even if I’m in a quiet setting. Apple says that situation will improve as Siri adapts to the way you speak. Its logic isn’t entirely foolproof, either. When I asked it to “call dad,” it presented me with three dialing options: “Dad work, Dad home, or [colleague] Adam Lashinsky.” (For the record, Adam and I aren’t related.)
You also run into its limitations quickly, which will also be frustrating. Because Siri makes certain tasks much easier, you try to push the boundaries and figure out just how many tasks you can offload. You can look up movie theaters, but you can’t look up show times. You can send texts, though you can’t add contacts. Many of Siri’s shortcomings ought to be fixed in the future. It’s just a shame you can’t do more with it now.
In the end
Whether the iPhone 4S warrants a purchase all depends.
I can see why Siri is a big draw. Apple’s offering a tantalizing future: a simple, streamlined user interface where many interactions with the iPhone are conducted via voice. And what it does do, it often does well. (Looking up restaurants and booking appointments are a breeze now.) But Siri is clearly still in its early days, and for every task it can do, you’ll run into just as many situations where you’re better off navigating the “old-fashioned” touchscreen way. It feels like a smart, nascent piece of technology that can’t grow up soon enough.
If you own the original iPhone, 3G, or 3GS, you’ll enjoy the speed gains and quality camera. If you own an iPhone 4, the upgrade path is less certain, especially if you just bought a Verizon iPhone earlier this year. The improvements will seem far less dramatic and more iterative, probably because using the iPhone 4 never felt like a drag to begin with. Either way, there’s a lot to like, even if the changes are evolutionary, not revolutionary.