Mikhail Gorbachev storms out after Rocky's post fight speech instead of leading a round of applause - This is totally counter to his personality and a pointless change that makes the film worse.
Ludmilla Drago (Ivan's wife) is reedited to remove all scenes of her being visibly/audibly in love with him - I understand this is done to make her character change in Creed II more understandable, but it was better before and the idea that she changed is better than the idea she never loved Ivan or her son.
They removed Pauley's robot from the film - A lot of people see this as silly, and it is, but it is also an example of how money and lifestyle have changed Rocky. Removing it isn't so much of a problem but not replacing it with something that serves the same plot piece is a problem.
Ludmilla Drago no longer nonchalantly smokes as Apollo lies dying (the scene was moved to mid fight) - This is a bad change and doesn't even tie in with above, why make her less uncaring when you're trying to make her more uncaring...
Ivan Drago's character/story/presence is majorly changed to be less sympathetic, so instead of being a subservient puppet of the USSR who rebels against his masters and breaks free at the end only to fall short, he is now arrogant and self obsessed defying his masters for his own ego before turning on them at the end, which obviously makes him less likable.