By Will Goodbody, Science & Technology Correspondent

It's just over a year since HTC revealed the HTC One M8, the successor to its highly acclaimed HTC One flagship smartphone. As you would expect, building from such a solid base, the One M8 also received a good reaction, cementing HTC's place as a leading player in the highly competitive smartphone market.

So when the company revealed the One M9, another upgraded version of the award winning handset at Mobile World Congress earlier this month, it provoked some raised eyebrows, and high expectations. After all, it would have to be exceptionally good to convince fans who had upgraded within the past 12 months to part with potentially hundreds more euro to get the newest version.

So now it is about the be released here, how does the M9 measure up? Well, as has been the case with all versions of the HTC One, it looks lovely. The metal unibody now has the added feature of a dual tone - in the case of the review unit I had the body was silver and the rim gold. The power button has moved down from the top onto the right side, which in theory should be fine. But in reality it is a little irritating, as it looks and feels very similar to the volume buttons, which can be a cause of confusion. It is heavy, but has a feeling of robustness, and all told is certainly among the most attractive smartphones on the market.

The screen remains the same as on the M8 - it's 5 inches in size with a Full HD 1080p resolution, which is arguably a missed opportunity when so many other manufacturers are moving to Quad HD. It is rumoured, however, that next month HTC will unveil a larger screened version of the M9, this time with a QHD screen. Nevertheless, the M9's existing display will be perfectly adequate for most - sharp, with rich colours and very responsive to the touch. The only possible niggle is that the bezel, speakers, logo and body take up quite a bit of extra space around the M9's screen.

One feature that is new on the M9, however, is the camera. For the main camera HTC has ditched the impressive 5MP duo Ultrapixel sensor on the M8 and upgraded to a 20MP with sapphire cover lens. It record 4K video, boasts some new imaging editing features and all round is respectable enough. However, camera purists seem disappointed that HTC, which has a reputation for innovative developments in camera technology, has changed direction back towards what its competitors have been doing for some time.

HTC has also always made a point of emphasising sound quality on the One handsets, and this time it is no different. The M9 has received an upgrade, and now has HTC Boomsound with Dolby Audio for both the speakers and headphones, with impressive results.

Under the bonnet, the M9 is powered by the new Qualcomm Snapdragon 810 octa-core chipset backed up by 3GB of RAM, which all makes the Android Lollipop operating system, combined with HTC's Sense skin, zip along reasonably well, with just a little lag at time.

That new engine, combined with a considerably bigger battery, should make for better power performance. We weren't in a position to test the battery at great length, but reports suggest that given the upgraded hardware, it is a little disappointing. Nevertheless, HTC promises 22 hours of talktime and 402 hours of standby time on 3G.

When it comes to storage, HTC has gone with a fixed 32GB ROM in the M9, which can be extended by another 128GB via the microSD, which is impressive for those who store their life's work on their phones.

Aside from all that, there are some new features around the interface in Sense 7 and BlinkFeed, the addition of the Peel Smart Remote app for controlling your TV viewing and some other minor tweaks and changes.

To be clear, despite only modest changes, the HTC One M9 is still a very good phone. But it is expensive, and all-in-all the question remains: is there enough new in the M9 to coax existing One users to upgrade or to attract new users who otherwise might go the iPhone 6/Samsung Galaxy S6 or Sony Xperia Z3 route?

It's no certainty.

The HTC One M9 goes on sale here from March 31 through Vodafone, Three and Carphone Warehouse. SIM free it is estimated it will cost €749, but monthly contract deals are available through operators.