By Will Goodbody, Science & Technology Correspondent

For the past couple of years, Sony has been regularly churning out updates to its flagship Z series smartphone.

The Z3 was announced at IFA in Berlin last September. So the expectation was that an upgrade, most likely the Z4, would be forthcoming around the time of Mobile World Congress in March.

But it never materialised, raising further questions about Sony’s commitment to the mobile segment, which it had itself discussed in public.

Fast forward a few months, and Sony has finally released an upgrade. But it is not the Z4 as imagined, but the Z3+.

Most likely that is to manage expectations. Because the Z3+, while a typically solid handset, represents a minimal improvement on its predecessor.

It looks very similar to the Z3, which is no bad thing, built on a metal frame with tempered glass and rounded edges.

The only real design change being that at 6.9mm it is a small bit thinner than the Z3. It is also a little lighter, on account of the smaller battery, which is reduced from 3100mAh to 2900mAh.

Like its predecessor, it is waterproof and dust proof. But a significant difference is that the Z3+ features a capless USB port, which is certainly a design improvement.

The magnetic charging pin has also been removed, resulting in a sleeker design.

Sony’s smartphones have always been market leaders in imaging, and the Z3+ is no different. The rear-facing main camera remains 20.7MP, but the front-facing selfie unit has been upgraded to 5MP.

As you’d expect the main camera takes very good images indeed, even in low light, and comes packed with quirky (or pointless depending on your point of view) effect features. Indeed, Gourmet Mode will, apparently, take wonderful pictures of your grub!

Video recording on the main camera is 4K and Full HD on the front-facing lens.

The Android 5.0 operating system runs on a pacy Qualcomm Snapdragon 810 octa-core 64 bit processor, which is an improvement on the Z3. It retains the 3GB of RAM and comes with up to 32GB of internal storage, which is twice the limit of the Z3, and can be expanded via microSD to 128GB.

Although the battery is smaller than on the Z3, Sony still promises up to two days of life. And if you have a Qualcomm Quick Charge™ 2.0 certified charger, you can get one day usage with just 45 minutes of charging.

There’s also been an upgrade on the wireless connectivity front, with LTE Cat 6 and Wi-Fi MIMO bringing faster connection speeds of up to 300 Mbps on 4G.

The 5.2inch Full HD display remains the same, but is very good, despite having fewer pixels than quad HD handsets like the Samsung Galaxy S6.

Sony is pushing the audio features of the Z3+, like the inclusion again of High-Res audio, and DSEE HX, which upscales existing MP3s to near High-Res quality.

If you are a music connoisseur, listen a lot in a quiet environment or like wireless headphones, the audio features probably will make a difference. But for most, particularly those who consumer their music on the move, it most likely won’t be deal breaker.

The Z3+ also has the unique selling point of the ability to play PS4 games through the DUALSHOCK 4 Wireless Controller anywhere in the home using Remote Play over Wi-Fi. Something which definitely is attractive to gamers who like portability.

The Z3+ comes in single and dual SIM variants, and four different colours.

It is certainly something of an improvement on the Z3 and is a very nice handset. It also shows, for now, Sony’s commitment to continuing to compete in the high price segment of the market.

It does, however, lack both ambition and any new knock-out features. The changes are subtle, unlikely to mean a huge amount to the average user.

And that’s likely to weigh on its success as we wait patiently for the real Z4.