Sony's latest high-end phone, announced for the Japanese market, is a bizarre non-upgrade that does no favors for the company or its customers.

Let's talk about the Sony Xperia Z4. The Japanese electronics giant announced the latest in its line of premium Z-series smartphones recently for its home market. And it's fair to say the popular reaction to the device has fallen somewhere between bewilderment and outright derision. Consumers and critics alike seem confused as to why this phone exists, questioning the priorities Sony's taken with what appears to be its early-2015 flagship.

With questionable hardware priorities and no word of any global launch, it's a bizarre turn for Sony, coming as the company looks to restructure and streamline its smartphone offerings and focus primarily on the high end of the market. The Xperia Z4 can boast only a couple of meaningful improvements over its six-month-old predecessor, and in one or two important areas it may actually be a regression from the Z3.

A new phone every six months

Xperia phones

First, some background. Since 2011's Xperia Arc, Sony Mobile (and before it Sony Ericsson) has shipped a new flagship smartphone every six months. It's a strategy that's yielded mixed results for the manufacturer. In some cases it let Sony unveil phones with exciting new technology before anyone else — the best example of this was 2013's Xperia Z1, with its groundbreaking 20.7-megapixel camera and Snapdragon 800 processor. In other instances, it felt like a new flagship was being thrust upon the market just because. Sony's roadmap called for a new phone, it seemed, and one would arrive whether or not it had anything new to bring to the table. As good as the Xperia Z3 was, Sony missed the opportunity to drop any significant performance or feature improvements over the Z2 or Z1.

Nevertheless, that's the strategy Sony has adopted up until now, and in regions like Europe where it's an established mobile brand, high-end Xperias have continued to sell well. Admittedly, six-monthly product refreshes have done nothing to help Sony Mobile's floundering efforts in the U.S., where carriers prefer high-end handsets to stay on store shelves for a full year.

Sometimes the half-yearly cycle would allow Sony to be first with exciting new technology, sometimes it seemed a new phone would arrive just because.

So that's the backdrop against which the Xperia Z4 arrives. Industry watchers and Sony fans were expecting an Xperia Z4 soon enough, despite the device being a no-show at the usual launch platform of Mobile World Congress. And given that the Z2 and Z3 were relatively incremental upgrades, it was hoped that the Z4 would be the big, exciting new Sony phone to fend off challengers from Samsung, LG and HTC.

That's what makes the device we got — and the way it was announced — all the more strange and disappointing. Sure, it's faster on paper, with a beefy new Snapdragon 810 processor from Qualcomm. But it's been a long time since day-to-day smartphone performance had anything to do with the amount of CPU horsepower at your disposal.

For real users in the real world, two of the most important hardware characteristics are battery life and camera quality. Yet the Z4 sees Sony standing still in one area and taking a tangible step backward in the other.

Forsaking 'two-day' battery life

Xperia Z2

Over the past year or so, Sony has put a considerable engineering and marketing effort behind "two-day battery life" in its phones. With their hefty internal batteries, the Xperia Z2, Z3 and Z3 Compact could last much longer between charges than most competitors, and Sony took advantage of this lead in longevity in its advertising. Range anxiety is an issue every smartphone owner can relate to, making superior battery life an appealing differentiator for Sony's high-end phones. In recent months it's continued to push the "two-day battery life" line through long-lasting mid-range phones like the Xperia E4g.

With a smaller battery and power-hungry CPU, it's unlikely the Z4 will be able to match its predecessor's 'two-day' longevity.

Yet the Japanese Xperia Z4 announcement makes no such claims, and it's plain to see why. In the pursuit of ever thinner devices, Sony has lopped 140mAh off the Z3's battery, packing a smaller 2,930mAh cell into the Z4. Numbers don't always tell the full story, which is why it's worth looking at what other Snapdragon 810 phones are managing. The HTC One M9 just about achieves a full day of use on its 2,840mAh cell, while the LG G Flex 2 will do the same, if you're lucky, on 3,000mAh.

However efficient Sony's other components are, the Z4's CPU is a known quantity — a powerful chip to be sure, but also a power-hungry one. HTC has upped its battery capacity from last year's M8 to the current M9 by 240mAh and just about maintained parity in terms of battery life. It seems highly unlikely the Z4 will be able to match the Z3's stellar longevity with a smaller cell.

It's particularly unfortunate that Sony won't be able to boast of superior battery life with the Z4. The Android phone to beat in early 2015, the Samsung Galaxy S6, is a relatively weak performer in this area. In pursuit of a thinner smartphone, the company has arguably lost a much more important differentiator — and taken a step backward relative to its 2014 offerings.

Moving backward by standing still

Xperia cameras

Like the Xperia Z1, Z2 and Z3, the Z4 packs a 20.7-megapixel Exmor RS camera with a single LED flash and no OIS (optical image stabilization). Based on the specs listed alongside the Z4's Japanese announcement, this appears to be the very same IMX220 sensor Sony's been using in Z-series phones since mid-2013.

The lack of any serious camera hardware upgrade was a problem for Sony last year, and it's an even greater cause for concern in 2015, as the company goes up against the Galaxy S6 and iPhone 6, both of which are excellent mobile cameras.

Back when we reviewed the Z3 series, we reflected on the Xperia line's stagnation in this important area:

Despite token changes to the rear camera, the experience on offer is barely any different to that of the Xperia Z2, or even the year-old Xperia Z1. And while it's still a perfectly decent smartphone camera, Sony risks moving backward relative to its competitors by standing still in such an important area [...]

Ultimately what you're getting is still a pretty good smartphone camera, but there's no hiding the fact that Sony's 20-megapixel shooter is starting to show its age.

Sony's phones don't even get the best Sony camera hardware — that, it seems, is reserved for Samsung and Apple.

So it's surprising — shocking, even — to see Sony using a two-year-old imaging sensor in its latest phone, not least because Sony itself produces the advanced sensors used by the Galaxy S6 and iPhone 6. Samsung's latest uses an IMX240 sensor with OIS, the same one included in 2014's Note 4, while Sony also manufactures the iPhone's 8-megapixel iSight camera.

Both are better than the aging, OIS-less 20-megapixel unit used in the Z4, and we can only speculate as to why Sony isn't using its best camera hardware in its own premium handsets. Surely a company with a long history in photography knows that the camera is one of the most important parts of a modern smartphone.

Whatever the reason, Sony continues to slide further backward relative to its competition by standing still on camera hardware.

A conspicuously low-key launch

Xperia Z4 Japanese press release

Then there's the manner in which Sony revealed the Xperia Z4 to the world. There was no flashy global launch event, just a brief announcement from the company's Japanese arm. As for the possibility of a wider international release? Sony tells us it's "considering the feasibility in other markets," which at least leaves that door open. It's far from enthusiastic, though.

Sony can make amazing phones when it tries, but the Z4 just doesn't look like the company's A-game.

The Z4 announcement was conspicuously free from the kind of fanfare that usually accompanies a big product launch. And given the brand name being used here — Xperia Z4 — this would certainly appear to be a flagship phone. The mere existence of a device with this name in one part of the world is likely to slow Z3 sales elsewhere. Indeed, it seems unlikely Sony would want to deploy a brand with as much cachet as the Xperia Z line for a Japan-only product.

Sony will eventually have something to replace the Z3 internationally, and rumors are already swirling of a separate global flagship being in the works. The big question is whether it'll resemble the Z4 announced for Japan this week — a weird half-upgrade that might fall short of the standard set by its forerunner — or a more satisfying high-end smartphone. Because if this model is all it's got until the fourth quarter, we'd have to question whether Sony's heart is really still in it.

Sony can, and has, made amazing phones when it wants to, but the Xperia Z4 just doesn't look like the manufacturer's A-game. To get back on track, Sony should focus on two of the most important hardware characteristics of any premium phone — battery life and camera quality. If and when a new global flagship arrives, it needs to match the high water mark set by the Z3's longevity, while taking a confident step beyond the past two years of 20-megapixel Sony cameras.

If it can address these two areas, Sony's next big thing will be well-positioned to compete with its high-end rivals. But if it continues to stand still on imaging, and squanders its lead on battery life, it risks losing out to Samsungs of the world at a time when its premium smartphone sales are more important than ever.