I started a new Minecraft world after a long time, the last time being shortly after the update that added the new cave biomes and changed world generation and I'm instantly reminded of how useless copper is. Can't make tools with it, can't light torches with it, can't use it as fuel, and it's all over the depths you'd typically find iron and coal, the two early ores that actually do those things 
Those annoy me less since I'm not compelled to mine them unlike copper and the new rock variants just register as background to me. With ores I feel like harvesting all of them from my mineshafts for completeness' sake, especially since the shader I'm using adds a slight glow to most of them so they stick out. I already have chests full of unsmelted copper
What about how normal digging used to result in some stone, dirt maybe, gravel maybe, and now just going to mine fills your inventory up with seven different variants of rock ? I was already sick of having andesite and diorite and now there's like a different block for every existing block but it's deepstone or whatever. I hate how cluttered inventory gets three minutes into mining.
They really made mining suck a lot more than it used to, which is alright I guess because it encourages caving since branch mining isn't as good, but sucks because early game iron is super hard to find.
I don't like the new ore distribution. Redstone is also kinda hard to find. Gold for some reason was super easy to find in one of my worlds, but at least that's good for piglin bartering. I don't like how much you need to use villager trading to do normal stuff.
Idk why they couldn't put in copper tools that are sightly faster than iron, but a lot less durable.