Don't fix what isn't broken, one of the few cliches that still work.
I bet if people didn't know this wasn't Rocksteady studios they wouldn't even know the difference. It's like asking people to tell the difference between drinking bottled water and municipal water and then asking which one tastes better.
I'll rate this game high, I don't care. There is absolutely nothing wrong with Origins. If Arkham City were the third installment and this were the first one, then people would be making same complaints. I'll settle for the Uncharted 3 argument/syndrome but there is little to no reason to downgrade this game because it more or less features same core gameplay. And WHAT IS that "same"? Refined fighting system, satisfying action, old and new upgrades (that you have to actually work for this time around by completing challenges), expanded itnel/database, enigma's games, superb voice acting, crime investigations, top notch cinematics, joker's side of the story (a clock work orange), a plethora of new and old characters each of whom require a different takedown approach, the perma-death mode, among many other things, the horror!
There's little to no innovation? Well, for starters you can't innovate much when it comes to something that happened in the past. But there are small changes there and there. You can now slide into the grates and open them. You can daze your foes with smoke and they will swing their arms at each other and punch it each by accident. Many fights are no cakewalk. Many enemies become armed towards the middle of the game, the ninjas, the martial arts experts and Bane's brawlers can make fights quite tough. The environments are also more varied. There is still no blood splatter anywhere, however. Many fights requires preparation in advance - disable guns, check; disable gun crates check; mark the ones you want to bump together, check; throw the smoke pellet in the middle of the crowd, check; swoop in and start kicking ass.
The game is considerably longer than the other two. It took me 30 straight hours to beat it and I have only completed around 60% of the game. The game literally goes on and on.
The game is much more Tim Burton-y this time around. There are more highrise buildings so there is greater satisfaction of gliding and plunging down. The city is filled with gangs and crimes that you can prevent. The streets are wide so there is more maneuverability. There is more approach to targets. The old Arkham City area is filled with somewhat disturbing Christmas decorations. The art design is off the charts. I also like the fact that you are kind of on your own in a sense that cops and criminals don't really know what to make of you. The graphics are also somewhat expanded, noticably the lens flare, the smoke that adjusts to your movement and changes its shape (nonexistent on the consoles), and physx (ah, those snowflakes dancing around when you fight 10 people at the same time - the consolites are missing out), AND LET'S NOT FORGET THERE IS NO GAMES FOR WINDOWS LIVE.
Each boss fights requires a level of investigation, psychological build up and later on skill and patience - something that Arkham City wasn't too famous for later in the game (which was one of GS's gripes by the way). The ultimate bane fight was as close to the Mr. Freeze fight as it got. The uneasy alliance with Gordon was also played out pretty well.
I can only wish this was the first installment. Arkham City was pretty much a perfect game but it doesn't preclude Origins from being a great game.
P.S. Don't skip the credits scene.