"Exactly as tech reviews describe it"4.5 starson by LonnieMGreen
Pros: Battery life is surprisingly good
Very fast processing speeds
Call quality is decent
Air Gesture is actually pretty good
Screen is nice and large with very good resolution display
Cons: S-Voice is still notoriously bad
Can't use the SD card for apps right now
Limited to 16gb of on board storage
Summary: It's the S4. There are plenty of tech reviewers out there who have done full work-ups on all the different features, so I'll just hit the main points I noticed.
The battery life is surprisingly good. I've had a number of these types of phones before, ones that are "cutting edge", and most of them have terrible battery life. I've had my S4 for almost a year now and the battery life is still very good. I do charge it nightly, but if I forget I can usually make it almost 2 full days on the charge. This of course assumes I'm not playing any full-screen games, keeping the screen on for any length of time, or checking Facebook (all of which significantly drain every phone's battery). One point on this though is that I've got most of the special Samsung features like S-Voice, Air View, Smart Pause, Smart Scroll, NFC, S-Beam, Multi-Window, and Smart Stay turned off. I do however keep Air Gestures on. I also have Bluetooth off most of the time, only turning it on when I need it, and I use the Tasker app to automatically disable my WiFi when I'm not near known connections like my house, my friends' houses, etc. If you keep Bluetooth on all the time, or WiFi on for the "location support" provided by Google, you're looking at about a 25% reduction in how long the battery will last.
Samsung apps and features:
As pretty much everyone that's rated Samsung devices in the last 3 years has said, just turn them off unless you're showing them off to a friend. The "eye detection" that's used for the Smart Pause, Smart Scroll, and Smart Stay not only eats battery like crazy while constantly trying to locate your face and eyes, but is delayed and spotty under normal usage conditions. The Air View and Multi-Window only work with a few apps, most of which are ones I never use to begin with, so it's not worth the battery cost and responsiveness costs of having them enabled (especially the Air View that eats even more power trying to detect your finger before it even touches the screen). The Air Gesture is actually pretty good, depending on which ones you've turned on, but anything that involves scrolling or pausing basically doesn't work, get an app like WaveControl for that instead. All the scrolling and pausing stuff, when it even works, only works with a few apps, once again mostly apps I never use. The S-Voice is still notoriously bad, unable to detect almost anything correctly and having an extremely limited set of commands that can be used. The automatic wake-up feature of it also drains battery so fast you'll be plugging the phone in for a full recharge twice a day even if you don't otherwise use it. The contacts app was a huge step forward from Samsung's last one, actually allowing contact integration from sources like Facebook, Twitter, etc, and joining and splitting of contacts in a reasonable manner. It still seems to have a few problems with selecting the default source for a joined contact getting overwritten by the latest data source to update (so you'll almost always see the latest Facebook picture of your contacts rather than ones from Google+ if Facebook syncs more frequently like mine does), but that's minor and can be fixed by saving the picture locally and selecting the local contact as your default. The calendar app is also a huge step forward, integrating all your calendar sources well and providing a nice mechanism for setting all the important fields from multiple calendar sources. Somehow despite a lot of the stock app updates they provide that have better integration for the features of Android, they still have what I believe to be one of the worst launchers of anyone (the home screen settings, display, etc). The first thing you should do is go get the free Nova Launcher, Go Launcher EX, or ADW Launcher (or any other for that matter), install it, and set it as your default. Every launcher out there is better in almost every way from the stock one and has been since well before the S4 even came out.
Size and construction:
The S4 was originally touted as having a "very large screen", albeit smaller than the Notes do, and they weren't kidding. The screen is nice and large, with a very good resolution display. It's not as good as a retina display, nothing else is that sharp, but it is significantly larger. The phone itself feels solid, and the metal bevel around the outside edge gives it that quality feel previous models didn't have. The battery cover is very thin plastic, so thin I worried about tearing it when putting in the battery and SIM card the first time, but it holds up really well and is much more sturdy than it initially feels. The screen is virtually unscratchable, and doesn't crack even with rough use. I accidentally dropped my phone down an entire flight of concrete stairs a few months ago, without any case on it whatsoever, and all I got was a single crack along one corner that doesn't impede the screen at all and can't be felt when running fingers over it. After almost a year of use, the only noticeable wear effects were on where the "metal" bevel edges come up to the edge of the face. The "metal" parts are starting to wear off (I keep my phone in my pocket without a case so it's sliding in and out of my jeans regularly) and reveal the sturdy white plastic they're actually constructed of.
Overall I would highly suggest this phone for anyone looking for a new one, even over the Note 3 that's supposedly a newer and larger screened model (mostly because of the battery life).
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I hope this review is helpful.