David Phelan has exclusive hands-on time with the new iPhone

After a long wait - more than 15 months - the new Apple iPhone arrived on Friday. But initial reaction was more disappointment than delight. After all, it looks exactly like last year's model. So has Apple misjudged the public mood, or is the iPhone 4S, as it's called, a worthy successor to the iPhone 4?

To start with, the name is revealing. Apple knows it's a gentle upgrade - it could have just called it the iPhone 5 and plenty of companies would have done that - and has acknowledged it in the number. And let's remember that the iPhone 3G was followed by the 3GS with a near-identical design. Perhaps Apple is training us that it's not switching from one snazzy design to another every year.

The iPhone 4's look was spectacular, so sticking with it for another cycle isn't in itself a bad thing. But this is Apple, known for the most striking, cutting-edge designs which, once revealed, become benchmarks that others aspire to – there are still gadgets being released that are unofficially considered to be coloured "iPod-white". To leave the design unchanged is different from the way every other company works so it has surprised us. Firms like Motorola, Samsung and HTC bring out phones with an industrial design that has continuity from one model to the next, but they're never identical. Nor do they only release one handset every 15 months. Clearly any change must be waiting inside.

Last year, the iPhone 4 launched to great success apart from one aspect - the antenna. Many users found the phone's signal strength dropped if you held the phone in a particular way. Others thought the antenna was weak, so you'd look down and find one bar of signal strength or, worse, the word "Searching" which meant you had no data or call connection at all.

As regular readers of The Independent will know, I live in a house with so many girders in its exo-skeleton it's hard for cellular networks to penetrate. The strongest antenna is needed to get through. I'm happy to report that while the iPhone 4 struggled against the strictures of this live-in Faraday cage, the new antenna on the 4S has worked flawlessly everywhere I’ve tried it, even at home. No calls dropped, no iffy connections and no dreaded "Searching".

Apple has redesigned the antenna, which is still in the band that edges the phone. Now, the two antenna elements - one for cellular connection and the other for wi-fi and Bluetooth - can switch between functions seamlessly to provide better coverage. It works well, and for many will be enough of an improvement to be make upgrading to the phone a no-brainer.

The phone's processor is called the A5, the same nippy, powerful chip that keeps the iPad scooting along. Though the last phone wasn't slow, the speed increase here is unmissable, with apps launching instantly and tasks completing with a satisfying briskness.

The other big hardware change is the camera, and this benefits from the accelerated processor, too. The app launches and is ready to shoot fast, even allowing you to take a picture directly from the lock screen. The chip helps reduce shutter lag compared to rival cameraphones. What's more, the interval between shots is tiny. The new camera has an eight-megapixel sensor with a wide aperture to suck in more light. Better yet, this sensor has something called backside illumination - it may sound vulgar but it just means that while most sensors have wiring on the front, here it's placed on the back, out of the way of the light. This is a technology largely pioneered by Sony on its compact cameras and helps deliver great results. The iPhone's camera is now very strong.

You can now hold the phone more comfortably while you take pictures, too. Instead of destabilising your grip by arching a thumb around to tap the screen’s shutter icon, you can press the volume up button on the handset’s edge. This is a big step forward, though right-handers will note that the natural orientation previously was to hold the phone with the earpiece to the left while now it needs to be held the other way around. This takes getting used to. This button arrangement will work on the iPhone 4, too, once the latest software update is applied.

There’s also Siri, an advanced voice recognition program which wants to be your personal assistant. It’s not finished yet so it’s still "in beta" but it already does a lot. You can talk to it colloquially instead of formally: "Do I need an umbrella today?" tells Siri you’re after weather information. It’s deeply impressive when it works, but talk too fast or in a noisy situation and it struggles. It also needs a decent data connection – it won’t work at all without this.

Neat features include the way it integrates location information. So you can tell it to remind you to pick up milk when you leave work and when it’s spotted you’re out the door, it’ll tell you. This is very cool, though the software has a way to go before it’s perfect.

The new phone comes with the latest version of iPhone software, called iOS 5, out today, which I’ll be reviewing separately. Suffice it to say it’s a subtle revelation, and at a stroke makes the Apple system the neatest and best smartphone user interface.

Most smartphones last a day’s use without complaining, though some go on a lot longer (Nokia and BlackBerry stand out) and many much less. Apple has made the iPhone 4S last a good day, though you shouldn’t plan on giving up on daily charging any time soon.

It's still not perfect. Would it be too much to ask for a little localisation, for instance, so the phone has a section called Favourites instead of Favorites? The screen, though still the highest-resolution display available on any phone, with a detailed richness that almost startles, could benefit from a little more real-estate. Android still beats Apple in terms of flexibility in laying out app icons on the home screens – with iPhone you have to place them in rows from the top left corner to the bottom right. If you have wallpaper that would suit a gap in the middle of the screen, Apple can’t accommodate.

But this is a decent upgrade of a great phone. If you have an iPhone 3GS, you should upgrade today. The same goes if you have most other smartphones. For iPhone 4 users, though, it’s still a compelling improvement, especially if you had trouble with the antenna. Besides, who knows how long we’ll have to wait for the next one?