The difficulty is pretty intense early on, and that was also where I had most of my fun. Once you get a few of the health upgrades and the later skills, the combat stops being much of a challenge, but I guess that's the point of leveling up. That said, I thoroughly enjoyed the entire game, which is more than I can say for most AAA releases these days. I picked up the season pass too, because I definitely wouldn't mind playing some more when they release DLC. If there's a sequel in the pipeline I can't even imagine how much better it's going to be if they continue to expand on these mechanics and flesh them out even more.
The world's the perfect size -- I actually gathered every collectible, which is something I never, ever do in open-world games (who wants to nab 200 feathers?), but the relatively small size meant it wasn't particularly difficult to find them, and there weren't even that many. I have basically zero complaints; it's without a doubt the best AAA game I've played this year, and I'd highly recommend it to anyone interested in open-world action games.
Oh yeah, and the game ran flawlessly on my 780GTX at 2560x1440, all settings maxed (no ultra textures though, I only have 3GB of VRAM anyway). It's really good looking, and I didn't encounter any bugs or framerate issues, or other signs of a bad port.
When your "nemesis" shows up for a final showdown, it's awesome. Mine was a guy who'd killed me in the first zone about a dozen times before I'd mastered the combat, but I'd forgotten about him once I moved on to the next area. In the next area, I dominated almost every captain and warchief without much trouble, but seeing the face of the guy who'd terrorized me for my first 5 hours was surprisingly entertaining.
When you're fighting the Talons of the Hand, I'm not sure if everyone's experience is the same as mine, but my dominated warchiefs slaughtered them all without any real intervention on my part (I dominated a few of the arches around the outside). That, too, was quite rewarding -- I spent a fair while leveling them all up and making sure they were up to snuff.