So my impressions of this game having just finished it on Centurion (Hard):
I don't suggest playing on any lower difficulty. Its about 10-12 hours depending on how many times you die. You do not need to do the executions. You can kill enemies without executing them but you need executions to regenerate health, gain focus or bonus experience. It is way more than QTE, too. If you learn the animations you can anticipate the next move. Pressing the button before it lights up generates more points. The combat is much more engaging than it first appears. As you progress through the game you level up your skills with points you earn from generating combos. Each successful strike you land earns a combo point multiplier which resets any time you get hit. So the whole point is to string together as big of a combo as you can. Now, don't make the mistake I did and fail to level up your executions! You can level up focus, health, etc. but you can also purchase new executions! I went through the whole game without realizing that. I had one time where the game hard locked. A quick Xbox go home, start Killer Instinct and restart Ryse solved the problem. If you are digital, swapping games is lightning fast. I loaded up the Legendary difficulty and started playing and it is extremely difficult. You have to have mastered the combat, especially deflection in order to succeed here. There are hits / deflects and then perfect hits / deflects. Essentially if you don't get a perfect deflect you're going to get hit on Legendary -- and it hurts! After spending about an hour dying over and over, I suspect finishing Ryse on this difficulty will be a significant bragging right.
I swapped over to multiplayer and this has some replay value. Its the same basic idea as multiplayer in Mass Effect except it is just 2 people. You fight in the Colosseum in completing various objectives based on themed areas from the game. You earn gold in this mode which can be used to purchase upgrade packs. You can upgrade sword, shield, armor and potions. I played that for a couple hours today and I'd like to do it a bit more before I start working on Legendary.