From a design standpoint, the Galaxy S9 and S9+ don't stray far from the Galaxy S8 and S8+. They don't even look too different from the Galaxy Note8. The internal specs aren't anything to be surprised about either: 4GB RAM for the S9 and 6GB for the S9+. Both share the same processor (depending on the region they both boast either the Qualcomm Snapdragon 845 or the latest Exynos chipset). And the batteries get the expected boost of 3000mAh and 3500mAh.
The defining features of the S9 and the S9+ are the cameras. The 12MP cameras of the S9 and S9+ rival the iPhone X and are slightly better than Google's own Pixel 2.
The cameras are equipped with OIS (Optical Image Stabilization). This means two things: less blur from shaky hands and more stable video recording. For improved low-light shots, Samsung has integrated F1.5 and F2.4 dual apertures. The S9+'s second camera telephoto lens also has F2.4 aperture.
The coolest thing about the S9 and S9+'s cameras is the Super Slow-Mo. At 960 frames per hour, the feature works by selecting the "Super Slow-Mo" option. Any movement that passes through the box will kick in Super Slow-Mo and it is amazing. You can make all sorts of awesome and fun videos with this.
Along with the improved camera is Samsung's take on augmented reality: AR Emoji. At its base form, it is just like Apple's Animoji on the iPhone X. The implementation feels and looks rough. It's nowhere near as accurate and detailed as Apple's tech, and feels as if Samsung rushed the entire feature.
You can also create your own 3D animated avatars. The front camera will scan your face and give you a rough representation of your digital self. You actually look like a Sim! You can customize the avatar with accessories and clothing, like Nintendo's Mii.
Another "big" change Samsung did with the S9 and S9+ is the re-positioning of the fingerprint sensor. Back then, the sensor was placed on the side of the camera, which became subject to online mockery. This time around the sensor has been placed beneath the camera, which should be easier for most people to use.
Shifting focus to security, the S9 and the S9+ use fingerprint sensors, iris scanners, facial recognition, and the usual stuff like PINs and patterns. There is also a feature called Intelligent Scan, which sets up the device to use both iris scanner and facial recognition. It works under low light areas and won't trigger on pictures of yourself.
The Samsung Galaxy S9 and the S9+ are impressive devices, despite being more of a refresh of an older model. This only pumps up the anticipation that Samsung is working on something even bigger, presumably the Galaxy Note 9.
If phone cameras are important to you, then you should start saving for the S9 and the S9+, because from what I'm heard, these phones are going to be a lot more expensive than previous flagships.