We wondered where the world’s number one smartphone maker could possibly go with the Samsung Galaxy S5. The Galaxy S4’s 5in screen was already hitting the pocketable limit, and with so much tech already squeezed into that phone there surely wasn’t much room for attention-grabbing extras. We were wrong. See also: the 11 best smartphones of 2014.

Still, cast a glance over the S5’s key specs and you might come to the same conclusion. Aside from the usual processor upgrade, from the quad-core 1.9GHz Qualcomm Snapdragon 600 of last year’s model to the top-of-the-range, quad-core Snapdragon 801, there’s no whizz-bang upgrade to match the quirky duo-camera of its major rival, the HTC One (M8), nor a radical rethink of design.

There are some differences. The plastic panel at the rear has changed from gloss to soft touch, there are new colours to choose from – including a dubious-looking gold – and Samsung has bumped up the screen to 5.1in.

Below the screen is a physical home button, flanked by two capacitive buttons; one for back and another for accessing the recent apps list. The display remains ringed with a ridged, chrome-effect band, with the power and volume buttons in the same positions on the right and left edges. The rear panel is still removable, giving access to SIM, microSD slots beneath, and a user-replaceable battery.

A closer examination of the specs reveals that the new phone is 15g heavier, and a touch taller and wider. For a more radical comparison you need to sit the S5 next to the HTC One (M8); the S5 is lighter, shorter, slightly wider, and – to our eyes at least – far less attractive.

Yet Samsung has made a number of changes: mostly small, but which add up to a major upgrade overall. Flip the rear cover off and examine the underside of the thin plastic back, and you’ll see evidence of the S5’s water- and dust-resistant protection: a thin rubber strip sealing in the sensitive components.

The Samsung Galaxy S5 is IP67 rated, which indicates the phone is protected against dust ingress, and can be submerged in water up to a metre for 30 minutes. Anyone who has ever dropped their phone in the sink, bath or toilet, or who’s soaked their phone in a heavy rainstorm, will attest to the fact that this is a feature well worth having.

The familiar home button hides another new feature: a fingerprint reader for unlocking the phone, similar to that of the Apple iPhone 5s. It’s less convenient than Apple’s touch-recognition approach, though. Only three fingerprints can be registered, and you need to swipe your finger across the button for it to work. As a result, we found it tricky to unlock the unit one-handed.

Then there’s the heart-rate monitor, located just below the camera on the rear of the phone. This is more sensibly positioned. With the phone cradled in your left or right hand, the sensor falls nicely under the ball of your index finger. However, heart-rate sensors work best when they’re constantly monitoring your pulse during periods of exercise or day-to-day activities. With the S5 you have to make a conscious decision to measure your pulse, which makes it less useful.

It’s the improvements to the phone’s camera that prove the most compelling. Samsung has upped the resolution to 16 megapixels, added DSLR-style phase-detect autofocus, the ability to shoot video at up to a 4K resolution, and is now using a new 1/2.6in sensor. The latter isn’t only larger than the HTC One (M8)’s 1/3in offering, but also boasts new “ISOCELL” technology aimed at reducing image noise.

The result of these changes is top performance and superlative image quality all round. The autofocus system, true to Samsung’s claims, focuses from near to far subjects in around 0.3 seconds – but that isn’t the full story. It can take as long as a second to analyse the scene before that focusing takes place.