Samsung has been on a roll. The success of its many models of smartphones, aided by massive marketing campaigns, has made it by far the leading maker of devices running on Google's Android operating system and the chief rival to Apple in smartphones. In fact, Samsung is almost as synonymous with Android as Google.

Now, the Korean electronics giant is about to launch its latest flagship phone in the U.S., a market where it hasn't been able to dislodge Apple's iPhone as the leader. The new model, called the Galaxy S 4, will roll out over the next week at AT&T, T-Mobile and Sprint, and likely sometime in May at Verizon Wireless.

I've been testing the Galaxy S 4 intensively for four days and while I admire some of its features, overall, it isn't a game-changer. It's an evolution of the prior model and despite some improvements, it still is especially weak in the software Samsung adds to basic Android. I found Samsung's software often gimmicky, duplicative of standard Android apps, or, in some cases, only intermittently functional.

I urge readers looking for a new Android smartphone to carefully consider the more polished-looking, and quite capable, HTC One, rather than defaulting to the latest Samsung.

The new Galaxy boasts a giant 5-inch screen, a bit bigger than the 4.8-inch display on its predecessor, but its mostly plastic body is thinner and lighter. It may stretch some small pockets and purses, and look funny when held to your ear, but it doesn't feel like a brick.

Still, compared with the iPhone 5, with its 4-inch screen, the S 4 is 30% larger and 17% heavier. The new Galaxy has a 13-megapixel camera, compared with 8 megapixels for the iPhone 5.

Nearly all Android phones already come with two email apps -- one reserved for Google's Gmail. But on the Galaxy S 4, there are also two online video and music stores, two music and video players, two calendars and two browsers.

Yet out of the box, there's no camera icon on the lock screen so you can immediately take a picture. (You can add this feature, via the settings menu, in -- you guessed it -- two different ways.)

Some of Samsung's new software features worked well. A feature called Air View lets you see expanded information about things like email previews and calendar items by hovering over them with your finger. A multi-window feature splits the screen so you can view two apps at once. But both features only work with certain apps.

I also liked an improved version of Easy Mode, which substitutes the sometimes confusing normal screens and settings panels for simpler ones with larger, cleaner icons and simplified settings.

Another good move: Samsung rewrote the standard Android email app so it's better, with a unified inbox and other nice improvements.

Speaking of settings, Samsung is proud of an expanded panel of one-touch settings icons you can get to by pulling down the Android notification window from the top edge of the screen. I liked the idea, but this panel is likely to confuse users with items labeled 'Air Gesture,' 'Smart stay' and 'S Beam,' and other special Samsung features.

There's an array of new camera effects, such as one where you can superimpose for fun a small square image of your own face onto a picture you're taking, and another where you can create a 'Drama' shot in which a single moving person appears multiple times in sequence. These are easy to select, but I doubt they'll be used frequently.

I had almost zero success with a suite of features that claim to take certain actions by detecting whether you're watching the screen. For instance, Smart scroll will scroll the screen based on the angle of your head and Smart pause will stop playing a video when you look away. I only got these to work about 10% of the time. Samsung blamed lighting conditions, even though I used it in many settings.

On many key hardware specs, the Galaxy S 4 shines. Its screen and camera resolution beat the iPhone 5's and I found its pictures to be slightly better than those from the Apple phone, which is nearly a year old. Its removable battery gave me a full day of use.

But the plastic body felt a bit insubstantial to me and the mono speaker on the rear was only fair. Oddly, I found the sound via headphones to be too soft in some cases, though voice calls were clear.

Prices will vary because T-Mobile has stopped subsidizing smartphones and Sprint has a temporary new-customer discount. But AT&T will sell the base 16-gigabyte model for $200 with a two-year contract. T-Mobile's price, paid over two years, will be $630, $50 more than the iPhone 5. Verizon hasn't provided details, according to Samsung.

My test model was running on the T-Mobile network and even indicated that it was using super-fast LTE, which T-Mobile is still building out, in some areas. But data download speeds in the D.C. suburbs averaged just 6.96 megabits per second, versus 20.81 mbps for an iPhone 5 running Verizon LTE. The Galaxy S 4 would likely be faster on Verizon in the same location.

While many will compare the Galaxy S 4 with the iPhone 5, I also compared it with the $200 HTC One, which came out April 19. The HTC has a handsome, sturdier, aluminum body, dual stereo speakers, an excellent camera, better screenresolution than the new Samsung and twice the base memory for the same price.