Smartphone companies can live or die based on the sales success, or lack of it, of their "flagship" phone -- as HTC found to its cost when the HTC One wowed reviewers but under-wowed consumers -- so all eyes will be on Barcelona in Spain when Samsung unveils it Galaxy S5 this week.

The South Korean company's S4 sold well, but not spectacularly, so there's a lot riding on the shoulders of the S5, not least of which is Samsung's position of as the world's largest and most successful purveyors of smartphones.

It has to hope the Galaxy S5, with whatever new bells and whistles Samsung has found to include in it, can convince consumers to shell out for yet another new and expensive smartphone when whatever is in their purse or pocket is likely to serve them perfectly well for the foreseeable future.

Smartphone technology has matured, some even say peaked. In the same way a PC that's a few years old is still eminently usable, so is last year's smartphone -- or the one from 2 years ago.

No phone app or software is so demanding it can't be handled by any phone offered in the last couple of marketing cycles.

That means Samsung's new phone may have trouble inspiring "must-have" feeling in consumers, leaving the company to hope it can create a "must-want" feeling.

So what's its game plan? Rumors abound as Barcelona awaits.

One is that the plastic look and feel of some previous Samsung offerings, which turned off many potential customers, will push Samsung to go with a phone chassis in the S5 with at least some metal elements.

It's more a cost factor that a design one, and plastic lets Samsung keep costs down and profits high. Still, when faced with the premium build of competitors like Apple's iPhone and even, yes, the HTC One, Samsung may opt to go with a little metal "bling" to crank up consumer desire, playing on the "look what I can afford" image a flagship phone can offer.

When it comes to a user's interaction with their phone, the display is everything, of course, so Samsung will have to up the ante there to keep up with the industry's march to ever bigger and higher-resolution screens.

The Galaxy S4's 5-inch 1080p HD display is as good as anyone might want -- remember "mature and peaking" technology? -- but Samsung will have to offer something beyond that.

The industry's next display milestone is likely to settle at an ultra HD display resolution of 2,560 by 1,440 pixels, and the S5 is expected to feature such a display.

Phone screens have been getting larger year by year, but if Samsung goes much beyond the 5 inches of the S4's display it would be venturing into "phablet" territory and thus risk cannibalizing sales of its own Galaxy Note 3.

Under the hood -- and of less interest to many customers -- the S5 is rumored to have settled on the Qualcomm Snapdragon 805 chipset, running at 2 GHz or possibly higher, a 3,000mAh battery, storage choices of 16GB, 32GB or 64GB and 3GB RAM.

Pricing is likely to be in the same ballpark as the S4 -- around $600 or $700 unlocked or $200 with a carrier contract -- with of course a bump to capitalize on "must-have" or "must-want," whichever Samsung can manage to create.

So, "quantum leap" or "incremental improvement?" This week will tell.