The South Korean firm warned earlier this week that it expected its profits to fall for the second quarter running.
Several analysts suggest the high-end market is becoming saturated, meaning most people wanting a premium phone already own one, making it harder to sell them another.
“Year to date, the share price of Samsung Electronics continues to underperform both in absolute terms and against the Kospi [Korea Composite Stock Price Index] as well,” Taewoo Kim, portfolio manager of Fidelity’s Korea fund tells the BBC.
“This weak performance reflected investors’ concerns on its smartphone business particularly in the high-end segment as a result of elevated competition.”
But Mr Kim believes things are about to improve, thanks in part to the improving performance of Samsung Electronic’s memory and home appliance divisions.
The new Galaxy could guarantee such a turnaround if consumers warm to its water-resistant build, improved camera and fitness-tracking facilities.
To mark the S5’s global launch the BBC asked five experts for their thoughts:
Chris Hall, Pocket-lint
The Samsung Galaxy S5 plays it safe on design, sticking to a tried and tested formula with its plastic body and chrome-trimmed finish.
There’s plenty of grip around the back and you still have the advantage of being able to change the battery, both to the phone’s credit.
Under the hood Samsung has packed in all the latest technology to make this a powerhouse.
There’s raw processing power and battery performance to get you though the day, fronted by a stunning 5.1in (13cm) display, with a camera that offers nice vibrant photos and the option for 4K ultra-high definition video capture, ready for the next generation.
But the implementation of the fingerprint scanner isn’t as tidy as the iPhone and we’re not convinced that the heart rate sensor was a feature that anybody was crying out for.
There is a huge number of features on offer making for a super-connected device, but we feel the user interface could be a little slicker and faster.
The Samsung Galaxy S5 is undoubtedly a great device, we’re just not convinced it’s the greatest.