Of course, the classic era is great and there's more to like than to not like, but are there some things, if any things, you're kinda glad they dropped and didn't go on with?
I'll start of with two things that comes to my mind:
Mean Hardass/Jerkass Apu: I like Apu, but I have to say that I don't really like the mean jerk Apu. He wasn't always like this, but when he was I wasn't a fan; for example he was shooting at people from the Kwik-E-Mart roof with a rifle at one point and was partying along with Sanjay and celebrated that Marge, whom he referred to as "bitch", was going to prison for 'shoplifting' from his store in 'Marge In Chains'. I like that they toned him down a bit and made him nicer later on.
Smithers enmity towards Homer: In some cases, this was pretty evident such as sometimes sternly telling Homer to shut up when speaking infront of Burns and chuckling in a evil manner as he banned Homer permanently from the SNPP's baseball game events per Burns' request in 'Dancing Homer'. I like it better when he is more indifferent towards Homer and does not have an outright dislike for him.