At first glance, the new batch of iPhones appear to adhere to what we've come to expect from an evolutionary update but as the saying goes, looks can be deceiving.

Apple first introduced the iPhone "s" variants in 2009. The label stood for speed back then, but is now indicative of a "tock" in Apple's annual tick-tock release cadence. S models are typically characterized by modest refinements, and while they traditionally afford at least one defining feature – the iPhone 4s introduced Siri and the 5s delivered Touch ID – they aren't known for generating the same sort of fanfare as generational updates.

The iPhone 6s and iPhone 6s Plus share much of the same hardware as last year's models, though there are some noteworthy differences. I'll be examining the larger of the two here today, a space grey iPhone 6s Plus with 64GB of storage.

The iPhone 6s Plus features the same 5.5-inch LED-backlit Retina display as last year's model, sporting a resolution of 1,920 x 1,080 that translates to 401 pixels per inch. Other display specifications include a 1300:1 contrast ratio, 500 cd/m2 max brightness and a full sRGB color gamut.

The big takeaway here is that Apple continues to use a 1080p display at a time when much of the flagship-level competition has moved to 1440p panels. The merit of that decision is worth considering: 1440p displays include 78 percent more pixels than their 1080p counterparts. More pixels translate to a sharper display, but the tradeoff is that it takes more processing power - and in turn, more juice from the battery - to push those extra pixels.

We'll see how having to push fewer pixels affects performance in a bit but in terms of visuals, the iPhone 6s Plus' display looks great. Images and text are incredibly sharp without being oversaturated. Brightness levels are also quite acceptable; in a side-by-side comparison with last year's 6 Plus, both displays look virtually identical and exhibit the same maximum brightness levels.

Powering the new iPhones is Apple's own 64-bit dual-core A9 "Twister" SoC clocked at 1.85GHz with 2GB of RAM on tap. Apple has also embedded its M9 motion co-processor directly into the SoC, allowing it to remain on at all times.

A dual-core chip with 2GB of RAM seems slow by today's mobile standards but we must remember that this is a highly optimized solution that's built specifically for iOS (and vice-versa). Factor in the lower resolution display and Apple's claim of a 70 percent faster CPU and 90 percent faster GPU (compared to last year's A8) might not be all that far-fetched.

This year's iPhone 6s and iPhone 6s Plus are offered with your choice of 16GB, 64GB and 128GB of flash storage in silver, gold, space grey and a new color, rose gold. Curiously enough, the 16GB option is still hanging around and hasn't yet been replaced with 32GB. Given the continued proliferation of apps as well as the camera upgrades, those opting for the 16GB model will almost certainly run into storage concerns sooner or later.

Pricing for the iPhone 6s starts at $649 off-contract and $749 for the larger iPhone 6s Plus.

Design Changes for Durability

Aesthetically speaking, you're not going to find much that is different with the new iPhones at first glance but once you dig deeper, there are a few subtle - but important - improvements.

The first major change is a shift to a stronger 7000 Series aluminum alloy for the chassis, the same material used to build the Apple Watch. After last year's bendgate fiasco, overblown or not, it's clear that Apple wants to put to rest any concern that its phone may be lacking in the durability department. Early bend tests from Square Trade vouch for the added rigidity.

The iPhone 6s Plus measures 7.3mm thick - up from 7.1mm a year ago - and tips the scales at 6.77 ounces (192 grams) versus the original Plus at 6.07 ounces (172 grams). The additional weight is noticeable although the added thickness probably isn't enough to warrant a new protective case for those upgrading from last year's model.

It's uncharacteristic for Apple to put out a new phone that's both heavier and this thicker than its predecessor. So, what gives?

The new aluminum is only a minor contributor as it adds just two grams to the 6s Plus. Rather, it's the 3D Touch-enabling display that weights more than twice as much as the previous panel. With that kind of compromise, Apple must be pretty confident in its new Apple Watch-inspired technology.

Speaking of the display, it's coated in a sheet of glass that uses a dual ion-exchange process to make it stronger on the molecular level. Apple clearly hasn't managed to find a manufacturer that can produce the hardened sapphire glass it wants to use following the blunder that was GT Advanced Technologies.

Touch ID, new camera and secret water resistance

Apple's fingerprint authorization system built into the Home button is back and better than ever. In fact, it may be too good. Touch ID is now incredibly fast, unlocking the phone almost instantaneously. This presents a problem when you simply want to check the time or a notification on the lock screen and may force you to use an unauthorized finger or press the power button to do so without unlocking the phone.

Something else that's been upgraded is the rear iSight camera. Apple has traded in its 8-megapixel rear shooter for a 12-megapixel variant with 1.22µ pixels, offering 50 percent more pixels than before. The camera features a five-element lens with f/2.2 aperture and a sapphire lens cover. There's also the familiar true tone flash and optical image stabilization although the latter is only a feature of the 6s Plus.

In addition to being able to capture panoramas up to 63 megapixels in size and 240 frame per second slow motion videos, the iSight camera can for the first time record clips in 4K quality at 30 frames per second. It's a welcomed addition but in this category, the iPhone is simply playing catch-up as other handsets have had 4K capabilities for some time now. Ironically, the phone also can't play back 4K clips natively.

I suspect most will stick with 1080p recording as it offers smaller files and the ability to record in smooth 60 frames per second.

New for 2015 is a feature called Live Photos that combines photos with snippets of video. When enabled, you simply capture a photo as you normally would - the difference being that the iPhone simultaneously records a few seconds of video before and after snapping the picture. When reviewing the Live Photo, you can tap and press on it to activate the video clip.

Live Photos is pitched as a neat way to enhance a memory and in some circumstances, it does add value. More often than not, however, it's best left disabled.

What you're taking a picture of is just as important a part of the equation as how, when or why you're doing it. For example, Live Photos would be completely useless if you're taking a picture of a static object like a painting you want to buy or a magazine cover. In scenes involving people, you may only have a few seconds to get the shot. Adding a three-second delay between snaps may mean you only get one chance to nail the image. Did someone blink? Too bad. And in practice, capturing Live Photos just feels unnatural. Who holds the camera up for a couple of seconds after taking their picture? What you end up with is a video clip that shows you pulling the camera back down to preview the picture you just took or even footage of its trip back into your pocket.

Then there's the technical aspect. Live Photo videos aren't of very good quality and they consume much more space than a standard photo. Or in other words, it's little more than a gimmick. If you want to take a photo, then take a photo. If you want a video, well, capture a video.

The front-facing camera has also been bumped up to 5-megapixels. What's more, it uses the iPhone's screen as a flash which should help considerably in low-light scenarios. I'm personally not the type to take selfies but I know a lot of people do and for them, this will be a welcomed improvement. Why smartphone makers haven't yet made a habit of including a high-resolution front-facing camera in this age of selfies, however, is beyond me.

The rear camera is technically better than last year's model but perhaps not as much as you'd expect. Having larger images to work with is great for cropping and resizing purposes but in terms of overall image quality versus last year's camera, it's tough to spot the differences. I did notice on rare occasions that despite having correctly locked focus on my subject, the resulting image wasn't in proper focus. This was most common with subjects that were dark or not very contrasting in nature. I also wouldn't mind a tiny bit more saturation on captures photos although this is easy to add in post-processing.

Perhaps the biggest surprise of all with the new iPhones is the fact that it's secretly resistant to liquid. Apple has never mention this and it isn't listed anywhere in the official specifications, perhaps to deter people from intentionally dunking their phones or maybe because it didn't secure the necessary certifications.

In iFixit's recent teardown, the team discovered a gasket-like material that lines the perimeter of the phone just under the display. This was no mistake as the chassis has been reworked to accommodate the gasket. iFixit also found that every cable connector on the logic board has its own tiny silicone seal.

The teardown specialists came to the conclusion that the new iPhones aren't fully waterproof (that's rumored for the iPhone 7) but they are significantly more resistant to liquid than previous models. What this means is that if your device accidentally takes a dive in the toilet or you get caught in a rain storm, it has a better chance of survival than before.