The combat is difficult/annoying for a few reasons
-The companion AI is terrible and requires micromanagement in a lot of fights. Your ranged people will stand there in a dragon's face and not fall back to a safe distance, they can't seem to decide on a target and in one specific fight I had Cole, Cassandra, and IB running back and forth between two lesser enemies (who were on opposite ends of the battlefield) as a group attacking one and then attacking the other no matter how many times I switched to tactical mode and moved them/assigned them to attack the more powerful enemy in the middle, they would run off and start their dance between the weak ones (which kept appearing until the strong one was killed) right after. They also will often forget to use potions and require you to switch to them and do it manually.
-You can't set tactics like you could in previous games
-There's a LOT of combat
-You can't change your mapped abilities in the middle of combat and you can't use the radial menu to use other abilities anymore
-No healing magic and extremely limited potions
-When trying to target something on a higher elevation with certain types of spells, the spell wouldn't just pop up the cliff, you had to trail it around a hill or path like you were walking instead of aiming something.
-You also can't change weapons or equipment during combat...I hope your melee fighters don't need to attack something on an unreachable platform because that emergency bow will do you no good. 
-It seems like there are fewer abilities and spells than previous games (the "upgrades" pad out the skill trees and make it seem like there are more but...)
It's worth playing for the story, characters, role playing, and beautiful environments but I absolutely hate the combat. My advice is to keep it on the casual setting, bring a lot of warriors and one mage, and try to keep yourself overleveled. That way you wont have to take much notice of it most of the time.