Samsung has finally unveiled its flagship Android phone that has been the subject of much speculation and rumour since, well, the Samsung Galaxy S3 came out. The Samsung Galaxy S4 has been launched officially during the Samsung Unpacked event in New York City and it's a doozy.To be honest, much of the speculation rather spoilt the surprise as, yes, it does have a 5-inch full HD Super AMOLED display. And yes, it also has that marketing-friendly 1.6GHz octo-core Exynos 5 processor and 2GB of RAM, at least in the UK anyway (some regions will get a 1.9GHz quad-core Snapdragon processor instead). Of course, much has been said that it won't actually really benefit speed that much, rather power consumption and usage, but that will be tested further down the line.The phone also looks much like the leaked devices we've seen over the past few days in videos and pictures, although not with the dotty black front and white back. Clearly those devices were mixed and matched, as there will be both black (Black Mist) and white (White Frost) devices on launch, not a mish-mash of both. What those pictures didn't really convey accurately is how similar the SGS4 is in the hand to the company's former model, the Samsung Galaxy S3. If not a little smaller, regardless of the screen size.At 7.9mm thick, it's thinner than the Galaxy S3 and that includes an improved 2,600mAh battery.\u00a0It's a promising statistic considering that one of its current rivals, the HTC One, is fairly beefy at 2,300mAh, but thicker at 9.3mm.Corning Gorilla Glass 3 performs the same function as on the phone's older sibling and should keep the expansive surface protected from scratches.\u00a0Some haters may bemoan Samsung's use of polycarbonate (plastic, essentially) for the rear, and yes, it's the only aspect that cheapens the Galaxy S4, especially when compared directly with a HTC One's aluminium unibody or the glass of the Sony Xperia Z, but we're pretty sure that the ease at which it can be unclipped to replace the battery, etc, offsets any initial disappointment.It's also quite comfortable to hold considering the extended screen size. This is thanks to a tiny bezel on the sides and top.The SGS4 has a new feature called Air View, which will let you hover your finger over the screen, without touching it, in order to perform specific functions, such as to increase the size of thumbnails on pictures, for example, before selecting them. It's something we've seen on the Note previously.It has other uses too, including with a dedicated version of Flipboard, customised to make use of the feature, but they will be explained in more depth when we review the handset fully and have spent considerably more time with it.\u00a0There are also some cunning gesture controls, with which\u00a0you can swipe through screens using your hand without touching the phone itself, and likewise it will take a full test to discover the true benefit of that, if any.Another funky new feature is Smart Pause. Where the Galaxy S3 has basic eye-recognition functionality by which\u00a0it keeps the screen from dimming when it detects you are still looking at it, the S4 also uses eye recognition with video. If you look away from the screen, it pauses the video clip or movie you were watching, although LG pipped Samsung to the post, announcing the very same feature for the Optimus G Pro.Other control features with eye recognition are built in too, including Smart Scroll, where it will scroll up and down on a webpage if you tilt your hand, and will do so only if you're looking at the phone. Sadly, in the brief time we had to play with the phone - in comparison to a full test period - we could only scratch the surface of what this tech can do.The rear camera is of the much-rumoured 13-megapixels, while the front is a very welcome 2-megapixels. We're particularly pleased with this as it'll allow your family to see you over Skype without it looking like an 80s home video. Plus, there are some amazing camera-based features introduced for the first time.The mode wheel from the Samsung Galaxy Camera has been added, so that you can add effects to your photos more easily. We particularly like the picture-in-picture modes for stills and video - Dual Shot and Dual Recording. These allow you to add a shot or video clip using the front-facing camera - in several styles - to one taken with the rear, in real time. That way you can see your reaction at the time of the shot or recording. It's fun, and will probably be used by "the kids" more often than business people, but it's nice to see something new.Another of the new camera features that we're particularly impressed with, at least during our initial play, is Eraser Shot. It's a burst mode that, when activated will automatically remove unwanted moving objects in the background. For example, if you are taking a picture of a loved one and a pedestrian walks behind them, it will remove them entirely. It's magic and really works.Android 4.2.2 (Jelly Bean) is on board from the off and Samsung's tried and trusted TouchWiz user interface is heavily plastered over the top. There are a few key apps pre-installed or intertwined through the system, with the keyboard looking particularly effective. Our first impression is that this probably has its foundations in SwiftKey, which was rumoured before launch, and was the case for the Galaxy Note 2.\u00a0Another app is Samsung's own S Translator. Translation apps are big news these days and Samsung's goes one step further by being integrated in the operating system so that, as well as offering language-to-language translation in app form, it will work in the email client and more.Other interesting technologies at work include Group Play, which allows up to eight Samsung Galaxy S4's in the same room to talk to each other independently of a home network. They can then all play the same music or take part in the same game (Asphalt 7 and Gun Bros 2 have been mentioned as examples).There's an IR blaster on board so you can use it to control any TV, not just a Samsung. IR looks to be enjoying something of a renaissance, being a feature of the new HTC One as well.READ: HTC One reviewFinally, for now, there's a pedometer built into the device, so combined with new app S Health, it can become a fitness aid, counting steps, calories, etc. It will also work nicely with Samsung's new range of wearable fitness devices, including S Band, but we'll feature more on them separately.Oh, and the SGS4 can double as an optical character recognition (OCR) device, to scan in text from a printed page. Phew.Depending on region, the Samsung Galaxy S4 will be a 4G LTE handset, of course. That includes the UK, on all the networks that offer, or will be offering, the enhanced services come June. It also has advanced NFC capabilities, including contactless payment and S Beam to share content between devices wirelessly, the spin-off of the native Android Beam feature.But bells and whistles aside, what will sell the Samsung Galaxy S4 more than any other aspect - more even than sheer brand loyalty - is the display. It is as vibrant as ever before seen on a Super AMOLED display, but with full HD (1920 x 1080) crispness to boot. That's 440ppi, for those that are counting, the same as the Sony Xperia Z.From our initial play, that's what has been burnt on to our retinas, for sure. Is it a major step up from the Samsung Galaxy S3? Probably not for many. But there's certainly enough that's new to promote it above being the Samsung Galaxy S3S.It should start to appear on networks and in shops from 26 April. Prices will be announced in due course.