Sony's latest mid-ranger, announced at Mobile World Congress, is a 64-bit waterproof phone running Lollipop out of the box

Xperia M4 Aqua

[custom:mwc15] Sony didn't surprise us with a new high-end flagship phone at Mobile World Congress this year, however it did introduce a solid new mid-range handset — the Xperia M4 Aqua. With a 5-inch 720p display and a plastic back panel, the M4 Aqua sits squarely in the middle of Sony's Android portfolio, between the Xperia E4 at the low end and the Z3 series at the high end.

A resolution of 720p might not sound particularly impressive in a market dominated by Quad HD panels at its most expensive price range, but the M4 Aqua's screen is not to be sniffed at. As HTC has done with its Desire series, Sony's shipping a somewhat lower-resolution panel, but one with bright, vivid colors that's still going to be more than good enough for most things you'll want to do on a phone.

On the outside, the Xperia M4 Aqua is the spitting image of Sony's Z3 series, sporting a metallic (though decidedly plasticky) segmented trim, Sony's trademark rounded power key and front-facing speakers flanking the display. The back panel too is plastic, furnished in a shiny polycarbonate that doesn't feel as premium as Sony's glass-backed Z3s. You might mistake it for a Z3 at a distance, but pick it up and the illusion quickly disappears.

That said, its build quality is solid, even if it lacks the premium materials we've come to associate with more expensive Xperias. At least you won't be sacrificing durability, as like much of Sony's smartphone lineup the M4 Aqua is water- and dust-resistant, rated IP65/68. Interestingly, Sony has managed to protect the M4's electronic guts from water damage without the annoying plastic flaps we've seen on the Z series phones. (SD and SIM slots are still hidden behind these plastic covers, however.)

Xperia M4 Aqua

Lurking within is an octa-core Snapdragon 615 processor, a capable mid-range chip we've seen powering the HTC Desire 820. With a 64-bit processor and OS, the M4 Aqua is Sony's first 64-bit smartphone. Snapdragon 615, combined with Sony's speedy software, makes for a fast, responsive user experience, at least on the demo units we used at MWC.

Xperia M4 Aqua

The M4 also gives us our first taste of Sony's Lollipop UI, which should be headed to existing Xperia Z series owners in the near future. Sony's redesigned portions of the software in keeping with Google's Material Design. The Phone and Messenger apps get a splash of color, and floating circular buttons for making calls and starting new messages. The redesigned Settings app brings more colorful icons, and the whole UI is animated in the manner you'd expect from a Lollipop phone. Apps like the Xperia Photos, Music and Video portals have received a bit of Material Design love too, including new icons and flatter UI elements.

Interestingly Sony's also dropped the Walkman brand from its built-in music player, a name featured prominently across its entire mobile range until recently. Not surprising perhaps, given that brand's diminishing value.

Xperia M4 Aqua

Sony has sought to differentiate itself through its camera experience and battery life at the high end, and this stuff appears to have trickled down to the mid-range too. The Xperia M4 Aqua packs a 13-megapixel rear camera and 5-megapixel front-facer, along with Sony's modular camera app. That means you get Superior Auto and Manual modes, along with fancier tricks like AR shot mode and Sweep Panorama. The jury's out on camera quality, as we were only able to use it under show lighting, but Sony's track record in this area leaves us hopeful.

Similarly, Sony has stood out in the past year thought its promise of two-day battery life for its high-end Xperia Z3 phones. It's making the same claim of the M4 Aqua, but we'll have to wait and see whether the bundled 2,400mAh cell is up to the task.

Either way, the Sony Xperia M4 Aqua looks like a promising entry to Sony's lineup, bringing a taste of the high-end to the middle of the company's portfolio. It'll go on sale this Spring, priced around €299 in the eurozone.