If Mega Man were to die tomorrow, Capcom would figure out a way to revive him. If the Street Fighters all succumbed to some obscure international plague, Capcom would find a way to make sure the tournament continued. And if Capcom decided to end a series themselves, we're guaranteed a sequel. That's what happened with Onimusha, and Dawn of Dreams proves why the promised ending after Onimusha 3 was the right way to go.
To their credit, Dawn of Dreams does try to separate itself. There is little mention of the previous games, and if they didn't exist, there would be no problem following the plotline here. The mission structure has changed; putting the gameplay inside strict levels instead of the open world we're used to. They've also implemented a hit or miss squad control that mostly ends up being a miss.
The key issue here is that these new additions defeat the point of calling this Onimusha. The linear levels are the largest complaint, restricting the player significantly, and causing a failure when attempting to refer to the gameplay as a "quest." It's hard to miss anything here.
Stages generally revolve around a puzzle, sometimes large in scope. With such a strict restraint on the player (levels rarely open up or branch out), the solution is generally easy, making these feel like work rather than entertainment. Given the game's epic and completely unforgettable opening, figuring out which switches to flip is a definite step down.
Re-spawning enemies curse what action is here. While a usual staple of the franchise, the puzzles here require the player to enter and exit countless doors, and bring with it more foes. This cheaply pushes the difficulty higher, and as one of the first in the franchise not to offer an easy mode, you'll be crushed.
It's even worse when dealing with multiple boss fights back-to-back. Without the ability to regain some health in between, rare yellow souls (which restore health as in previous Onimusha's) and cheap shots, winning is secondary to losing. Epic boss fights are here only because the developers made sure anything less than an hour spent slashing is a glitch. Many require the slaughtering of hundreds of Genma before the boss falls, simply because one or two attacks from the level guardian will drain an entire life bar.