The Samsung Galaxy S6 eliminates popular features its predecessors enjoyed. Credit: Samsung

When Samsung (NASDAQOTH: SSNLF) unveiled its new Galaxy S6 this weekend, it hailed the new smartphone as being "the result of the most significant team effort in the company's history." Samsung even code-named its development as "Project Zero" -- an apparent reference to its desire to design the Galaxy S6 from the ground up, focusing on what it believes is the perfect combination of aesthetic appeal, innovation, and practicality.

But in the process, Samsung also removed several key selling points that previously differentiated its older flagship models. Here are the three most significant features absent from the Samsung Galaxy S6.

1. Expandable storage
First, Samsung fans had grown to love that past Galaxy smartphones supported removable storage. In the Galaxy S5, for example, that meant users could supplement internal storage of either 16GB or 32GB with up to an additional 128GB on a microSD card.

Unfortunately, removable storage is no longer an option in the Galaxy S6. Instead -- and similar to the approach Apple(AAPL 0.51%) took with its wildly popular iPhone 6 -- Samsung will allow buyers to choose Galaxy S6 configurations with 32GB, 64GB, or 128GB of internal storage.

To its credit, that memory will be in the new Universal Flash Storage 2.0 format, which Samsung says is faster and uses less power than any other current external storage or internal flash memory technology. This means storage-sensitive tasks like taking pictures and playing games will happen more quickly and seamlessly than ever. 

2. Replaceable batteries
Next, Samsung opted for a sleek, seamless metal design for the Galaxy S6, as opposed to the more modular, plastic body of the Galaxy S5. But in addition to shunning expandable storage, that new design also meant doing away with removable batteries -- so no more expanded packs, spare batteries, or easy replacement of old or defective units.

Once again, though, Samsung offered some solace to jilted removable battery fans -- the Galaxy S6 has built-in wireless charging capabilities and is compatible with both primary wireless charging standards, WPC and PMA. Samsung also says the Galaxy S6 charges faster than any other smartphone and can top up in roughly half the time it takes the iPhone 6 to achieve the same feat.

3. Water resistance
Finally, the Galaxy S6 is not water resistant. This is not exactly a deal-breaker, as few other devices can claim the novel feature. But it is a notable step back from the Galaxy S5, which was water and dust resistant to IP67 standards, meaning it could be submerged in one meter of fresh water for up to 30 minutes. 

For perspective, Samsung boasted plenty about this fact in its marketing for the Galaxy S5 with commercials like this one:

That said -- and keeping in mind the Galaxy S6 will not officially be available until April 10 -- a "Galaxy S6 Active" variant is rumored to be in the works. If that is the case, it would almost certainly incorporate some level of water, dust, and shock resistance.

But whether Samsung dropped water resistance in the primary Galaxy S6 model for margin reasons or lack of demand, it will probably take some flak from consumers who have come to view this premium feature as standard issue.

In the end, though, it is hard to blame Samsung for effectively rebooting its Galaxy S line. The Galaxy S5, for its part, sold "just" 12 million units to consumers in the first three months following its launch, or around 40% fewer units than Samsung predicted at the time. Meanwhile, Apple obliterated all expectations by shipping an incredible 74.5 million iPhones in its most recent quarter.

To be fair, that included the launch of both the 4.7-inch iPhone 6 and the larger 5.5-inch iPhone 6 Plus, the latter of which competes more directly with the 5.7-inch Galaxy Note 4. But the fact remains that Samsung has significantly underperformed relative to its Cupertino-based competitor over the past year, and the Galaxy S6 arguably represents its greatest chance at redemption. But if Samsung cannot use the refreshed design of the Galaxy S6 to beat Apple at its own game, I fear that dropping these differentiating features could ultimately prove a huge mistake.