I have not finished the game but here are my immediate thoughts:
1. The combat is largely the same, but they made 1 HUGE change that can be a turn off for some, but a welcome challenge for others. Instead of being able to choose your skills to upgrade they now have a skill tree and most of the combat upgrades are locked away until you progress the story. This can be a HUGE disadvantage to people like me who made a living using the Critical Strike upgrade in addition to the instant takedowns, which enabled you to do instant takedowns and/or reach freeflow focus quicker. From a story and gameplay perspective it makes sense. Batman is young and raw and it makes sense to lock away his best upgrades until the end. It forces you to use the tools you have.
The combat also places a HUGE premium on the ability to counter. In principal it was also a good idea, but it has some problems that when combined with other problems becomes a major problem. Let me explain:
The camera in this game like the other games is still quirky. Too often the camera would get too close and you couldn't see many of enemies and you got hit because you couldn't see someone who was attacking. In AC it was annoying but I never felt it was something couldn't be overcome, but in this game it can be very frustrating. On top of that enemies in AO are MUCH more aggressive, the move faster and can attack you much quicker after doing an instant takedown than in previous games leaving you little time to react.
Where all of that really gets exacerbated is due to the fact that counters in this game have a difficult time registering. The knife counter takedown is one example where it only works about half of the time. In situations that require multiple counters it is downright rage inducing. Heck, even counter mashing doesn't work.
At the beginning of the game its a non-issue, but when you get to boss battles that rely on counters it becomes a problem. I thought maybe I had a problem with my controller so I went back and played Arkham City and had no issues, but then again having the ability to do critical strikes maybe just took the edge off.
Speaking of boss battles, they arent explained very well since its no always obvious when you are supposed to counter and when you are supposed to strike. The Deathstroke fight is a perfect example of this in which you are supposed to do counters, but there were times when the counter would do damage and there were times where I would end up taking damage. I never figured it out I just resorted to spamming my batclaw and that got me far enough.
Just my thoughts.