In a time where we have games like nier automata, nioh, bloodborne, Bayonetta 2 and even God of War, what I experienced with the DMC5 demo left me wanting more innovation and evolution.
Nier Automata has a cool world and story structure. The combat is about as trivial and button mashy as it gets.
NiOh has nice combat, but it's repetitive as hell and the combat strategy for each enemy is very similar. Ninja gaiden craps all over this game same devs).
Bloodborne is a faster souls. Again, it's not much of a character action game, but a good game nonetheless.
Bayonetta 2 is a carbon copy of 1. In fact I probably liked 1 more due to the novelty effect.
God of War is an embarrassment to anyone who played the GoW series for the combat. To me this was clearly evident when you get the blades, they just made the game go from a walking simulator to an action game.
Now as to your point. DMC5 is indeed an evolution of the genre rather than a revolution. The emphasis is on new weapons, mechanics, and playstyles. They wanted to keep the core the same and build on it. Dante looks nearly identical, but with crazier weapons. Nero has the breaker system, which is very innovative, lots of risk/reward and planning required. And V, this is completely new and innovative, where you control different beasts. Each character offers a vastly different playstyle. So for most people, there is plenty of novelty and innovation.
As for the demo, it was extremely limited. Maybe it's not that DMC5 is bad, maybe it's just a bad demo. It seems to me many people want their games more cinematic, and as a result, games like GoW with the stupid camera placement butchered the combat system. The majority of DMC games who appreciate the game for the combat system, want to keep it very similar. Why try to break a successful formula?
My suggestion is wait to see high level play before you (personally) get the game. If you care more about cinema or walking simulators, this may not be your cup of tea.