Very experienced Android user here, cooked or modified my own ROM's since WinMo 5.0, Pineapple on iOS, Cyanogenmod and others too. Coming from Galaxy S4 with 5200mah battery heavily tweaked for battery life, custom OS, etc.
OVERALL - This is the first 'no compromise' Active device, that has all the bells and whistles of the flagship S7/S7 Edge (minus S7 Edge 'Edge Screen features which i find pointless) and a bigger battery too; I love it. I feel no need to modify the OS in any way that would require root, or a 'compromised' bootloader. Get a glass screen protector ASAP; the polycarbonate screen cover will scratch easily, and maybe a very thin/slim TPU case for better grip and added safety in case of drops; they are cheap anyways; might as well for an $800 phone. Plastic and rubber sides and back mean no back glass cracking or breaking; my main concern with S7 and S7 Edge. Apple did away with glass backs and went to aluminum, chances are samsung will follow suit in a generation or two.
BOTTOM LINE - Get it, try it, use it, if you don't absolutely love it, take it back on the 13th or 14th day. Battery life is awesome, camera is wonderful, and its basically a Galaxy S7 with a case and larger battery that's far more worry free. Frankly, if you like the S7 or you are clumsy; get the Active. If you have kids, get the Active. If you prefer the Edge for its Edge Screen features, get the S7 Edge (and a case...). The Active makes the S7 somewhat redundant if you have AT&T. I bought 2 initially; one for myself (from an S4 with 5200mah Anker battery/case) and my GF; then bought another for my folks with an ancient Galaxy S3 (also on AT&T). First off, let it get used to your usage for a few days; app power saving lets you choose 'auto' or 'always' save power; i lean heavily towards 'always' save power. I installed Greenify and tweaked it for more battery life control, as well as App Killer Pro (Samsung) to disable AT&T bloatware and other misc stuff i wont use (Gear/Gear VR stuff, Facebook which i am not a member of, DirectTV, AT&T stuff). I also installed, but did not yet create any profiles with Tasker as well but that's a bit more in-depth.
Durability - A bit slippery out of the box (not as slippery as iPhones, S7, and S7 Edge); i bought an $8 TPU case on Amazon as well as a cheap glass screen protector to keep the polycarbonate screen protected from scratches; also $8 Amazon purchase. Held up to multiple water dunks while swimming and kayaking just fine. I wash it off regularly with mild hand soap and tap water, or windex and water, taking off the TPU case and wiping it dry then blowing water out of the charge and headphone ports and speaker; its seen dunks of at least 3 feet as well as left in my pocket whilst flipping my kayak or swimming and dragging my kayak out of lakes and creeks. Zero issues there.
Features - Activity Zone is useful if you hike/bike/kayak/actually ie DO stuff, S Health is useful as well if you track any of your stats as i do. You can program the button to launch 3 different apps to your liking. Camera is amazing (see below). Accepts and works with up to 200GB MicroSD cards (tested SanDisk 64GB/128GB/200GB UHS1 cards; haven't tested a 256GB yet), so storage isn't an issue. Fingerprint scanner is just as reliable as iPhone 6s/Plus and S7/S7 Edge in my experience.
Software - Excellent; Marshmallow 6.0.1 out of the box works great and really needs no tweaks, but i still use Tasker, Greenify, and App Killer Pro to extend battery life and disable features i wont use. Facebook app sucks down a lot of power; i dont use facebook (or any social networking, so that may affect your battery life) so I disabled it and its two reliant services with App Killer Pro as well as DirectTV and AT&T bloatware. First phone i don't feel the need to Root and ROM; i expected lag, stutter, and to end up returning it. While i still love my S4 with 5200mah battery, the S7 Active easily bests it and is more livable; faster and smaller 4000mah battery lasts longer, with less tweaks/customization needed.
Performance/Battery - Right up there with S7/S7 Edge in performance; specs are identical. Battery (FAR better than S7, and still better than S7 Edge) lasts 2 days easily; 44hrs (barely) 100%-1% with 8hrs (also barely) screen on time, GPS, NFC, Bluetooth, WiFi on occasion (WiFi saves battery vs LTE), with egregious usage of Camera and Google Maps and everything syncing whenever. Fast Charging and Fast Wireless Charging (Samsung Fast Wireless Charger) have it from 10% to 100% in about 2hrs 40 minutes. I Average 40 hours with 8 hours screen time with GPS, NFC, Bluetooth, and some WiFi usage in areas i get 2 bars of reception (low reception increases battery consumption; good reception and WiFi decrease battery usage). I try to use only the wireless charger so as not to wiggle/damage the USB port (S4 USB port died on me once), works flawlessly even with a TPU case on it. TPU case also only decreases signal by approximately 1-4dB, averaging closer to 2dB, and signal strength vs friends AT&T S7 Edge is on average 0.7dB lower vs S7 Edge with both naked, and 1.3dB lower with S7 Active in TPU case vs S7 Edge with no case. Both with TPU cases, or both naked, the signal dB difference is statistically negligible.
Camera - Second to none in mobiles from what i've played with; shoots RAW upon demand, OIS is ALWAYS on, HDR, etc. Flash is not bluish; its approx. 3600k (Kelvin), so a nice, clean, natural white. More options than you'll use, but clean layout. Pro mode RAW is impressive at 12-12.5 stops of DR (by my comparisons and tests); I film and photograph in RAW exclusively, professionally, and while this is nowhere near the caliber of some of the top performers i use in the pro world (at several to tens of thousands for a body PLUS lenses), for a mobile it is VERY impressive indeed, especially with having real OIS, which is Optical Image Stabilization, which in most the RAW film cameras i use, is non-existent or unavailable, and it REALLY works well, just as good as Nikon VR and Canon IS (their branded names for Optical Image Stabilization but is only built into certain lenses and none that i use regularly; this is the same tech...And it WORKS). AF tracking works as good as Nikon AF 3D tracking, and just as good in Video mode (but in 1080P mode only). Its also f1.7 aperture, and while the tiny sensor doesn't allow for very shallow DSLR depth of field, coupled with Always-On OIS it DOES allow for VERY sharp, nearly noise free low light shots. Jello is minimal for a CMOS sensor; very fast CMOS scan speeds, although clearly not a global shutter sensor.
Conclusion - Highly impressed and pretty surprised; If you're on the fence, try it. I even have the Gaudy Gold and im OK with it.