When the Apple Watch first began making headlines, the first question most people had was: "Is this watch going to replace my iPhone?" The short answer is no, it will not.
The Apple Watch was designed from the start to be a paired device. To get the best use out of your Apple Watch you will also need to own an iPhone. While some people may not see the point of having both, after a few days of using the Apple Watch, they will understand perfectly.
Style & Comfort
One of the great features about this watch is that you can choose from a whole range of different styles. Although the watch packs a lot of features and has good battery life, it does not feel too heavy or uncomfortable to wear. The watch communicates with the wearer primarily through a tactile interface, meaning it taps you to get your attention. As a user, you interact with the interface by tapping, swiping, and pinching on the touchscreen, and by using the "crown" device and push-button on the side of the watch.
Features & Apps
Apple has packed a lot of features into this small device, though of course most of them require connecting to the iPhone to deliver their functionality. Onboard devices include an accelerometer, heart rate meter, gyrometer, Bluetooth, WiFi, speaker, microphone, touchscreen, and of course the haptic engine that sends all those taps to your wrist.
In a pinch you might be tempted to use the watch as a phone, but that's probably less practical than simply using your iPhone for that purpose. It does excel in helping you to compose text messages however (which you will have to dictate, since there is no keyboard). Siri happily resides in both your phone and your watch and can do all the usual things you'd expect. You will find that you use Siri much more on the watch than you do on your phone, partly because you need to.
The watch comes preloaded with a lot of apps, and you can add more. In fact there are probably too many apps pre-installed, but you can remove the ones you don't want. There are far too many for me to describe here, but the most useful are probably Twitter and Maps, since these have practical applications in your everyday life.
Comparison with Samsung Gear
Head-to-head comparisons are not easy in this case, since all of the technology is so new and likely to undergo several updates in the near future. Compared with the Samsung Gear, the Apple Watch has a smaller screen and a slightly chunkier frame. Apple currently gives you more choice of styles than Samsung, while the price for the most basic model is practically the same between both brands.
Samsung's watch faces are bigger but some people may find them boring compared with the options available on the Apple device. The greatest advantage of the Samsung Gear is that it can operate all of its functions completely independently, while the Apple Watch is still largely dependent on the iPhone to provide many of its features.
The real decider here is probably going to be if you own or are considering to buy an iPhone. If that is the case, then the Apple Watch is a perfect accessory. Otherwise the Samsung Gear may provide the features you need. In terms of longevity and future expansion, the Apple Watch is expected to go the distance and will continue to get better.