Samsung Galaxy S4 review:

The Galaxy S4 handset steadily draws from the same design language as the S3, but takes almost every spec to an extreme -- the screen is larger (5 inches), the resolution greater (1080p), the battery capacity higher (2,600mAh), the processor faster (1.9GHz quad-core or 1.6GHz octa-core), and the rear-facing camera stuffed with more megapixels (13, to be exact). But, once you've gone through the features checklist (which also includes lots of internal and external storage space and RAM), it's the software extras that Samsung continues to lean on to keep its phones one step ahead of the competition.
At first glance, the Samsung Galaxy S4 looks like a cookie-cutter copy of the GS3, but larger. It has the same rounded edges and narrow physical home button as its predecessor, but at 7.9mm deep (0.31 inch) and 130g (4.6 ounces), it's also a little lighter and thinner. Part of the slim look and feel is a result of Samsung creating sharper, straighter lines with the phone than the GS3's subtle curves.
Standing at 136.6mm tall by 68.9mm wide (5.4 inches by 2.7 inches), the Galaxy S4 fits right in between the GS3 and the Galaxy Note phones. It's large, to be sure -- very large -- but since I've grown used to holding big handsets, it didn't feel overwhelming in my hands. A more dimpled finish on the white version I held reminded me of the Galaxy S2, in contrast to the GS3's silky brushed feel.

Turns out, that's somewhat true. Smart Pause and Smart Scroll are two features that build off the Galaxy S3's optional Smart Stay feature, which kept the screen from dimming when you looked at it. In the GS4, tilting the screen up or down while looking at it scrolls you up or down, say if you're reading a CNET story, of course. As a daily commuter with one hand on the phone and one on a hand strap, this could be a more convenient way to catch up with news while on the train or bus.

Eye-tracking gestures
Conflicting rumors painted a scenario where you'd scroll the screen with your eyes using eye-tracking software within the GS4.

I really like the idea of Smart Pause, which halts a video you're watching when your eyes dart away, then resumes when you start paying attention again.

Both features worked better in theory than they did in practice, though I should mention that the GS4 I was looking at is (obviously) preproduction running prefinal software. Still, response time was a beat slower than I wanted, taking a little time to pause and resume the video, and scroll the screen. A minor delay makes sense. You wouldn't want to start and stop again every time you're distracted for a second. Instead, the software seems to track longer periods when you're away, like if you stop what you're doing to order a cup of coffee, talk to a friend, or climb a set of stairs.

While the Galaxy S4 will look the same everywhere in the world, it won't necessarily have the same motor under the hood. Your future GS4 handset will either thrum from a 1.9GHz quad-core Qualcomm Snapdragon 600 series processor, or from a 1.6GHz eight-core chipset,Samsung's Exynos 5 Octa silicon.

Pricing and availability
If this phone sounds like something you want to get your hands on, you won't have to wait too long. Samsung plans to stagger releases worldwide in April and May. In the U.S., Verizon, AT&T, Sprint, T-Mobile, U.S. Cellular, and Cricket Wireless will all get the Galaxy S4 (along with Sprint MVNO Ting). Samsung hasn't yet shared plans for other countries.