For starters, the AI players are pretty garbage at doing anything and more often than not just literally stand there and let you blow by - couple this with atrocious and extremely predictible goalies, all the pressure is put on human defenders to stop everything.
Shot/pass blocks were slow to initiate (and I found the stick doesn't even touch the ice), hipchecks were annoying to pull off because of all the clicks and could lead to easy trips, poking gave you a huge nerf to speed, offense were given a hit immunity bubble when L2ing into and around the zone, and all defensive strategies are highly outdated. Just the tip of the iceberg.
It basically comes down to humans not playing the same way the AI is programmed to. We make custom plays while the cpu needs to do everything the "right" way and defensive abilities just aren't up to par with what offense can do.
No look passes from anywhere but are more dangerous from the corners, L2 ballerina deking everyone, ragging, goalies literally not moving on shots or giving predictible rebounds -- sure you can know its coming, but defenders risk putting the puck in the net with that many people crashing.
There are new goalie animations, hitting mechanics, and controls in 24 so we'll just have to wait and see I suppose