The endgame lacks the same level of excitement, it’s essentially the same as POE1, just more tedious. Personally, I find the gameplay most enjoyable in the first two acts, where the player’s skill and ability combos truly matter. The gameplay is more methodical, and mechanics like dodge roll actually have a significant impact. Later, though, it becomes about being overpowered and quickly clearing everything with a single ability. Boss fights are the best part of the game, but it’s annoying that not all maps feature bosses. The bigger the map, the more time you waste running through it, and less time spent enjoying the boss fights or content that’s more fun. What gets me is why do sooo many uniques have down sides with really really bad upsides at least in POE 1 in campaign uniques were huge increase in power here you aren't even hyped when one drops. Theres also skill balance issues.

PoEs biggest problem is itself. During normal campaign they set the bar super high with the boss fights. Overcoming the challenge felt amazing. Boss maps are the exact opposite of this. Even if a boss was challenging it wouldn't feel good it just feels bad when you die full stop because you only get 1 attempt. There's no challenge to overcome either because their either is no challenge or because you don't have the opportunity to overcome it. Boss maps would be a lot better if they were the only thing in the map, that's it.. just a boss to defeat. Except it was actually challenging but you get to keep trying and you have to defeat it to complete the map.

The way stone system isn't sitting right with me. I can see a massive problem for new and/or casual players that don't instantly take to maps in that they won't sustain tier 1 and will run out of stones. Sure you can buy them but if people are spending gold on them and still struggling they're just going to quit. And we should want end game to be accessible to these people. Further, needing to use another stone if you fail a map doesn't work because if that map is killing you and you've lost its events anyway you're just going to throw a tier 1 in it instead and cheese it.
I'd like to see the stone system changed so that normal maps don't drop and they just drop double affix magic. Having to use orbs on normals is kind of pointless anyway and isnt adding anything. Then allow people to run a map without a stone and if you do its just a tier 1 normal map. That way newer players can't run out of attempts. But, make it so if you fail a map you don't need to use another stone BUT the map remains locked to the stone you used on it but resets and you lose the events such as ritual etc.

Bring back the feeling of bosses from campaign.

Also, as well as doing some balancing for power creep end game.. makes the tiers go way way way way higher so the top players can compete for highest tier achievements on a ladder. Whilst everyone else will be fine doing lower tiers anyway. Think greater rifts from diablo 3 but with maps.

Also the lack of introduction and explanation of end game is really bad. I get there is a lot going on but at the very least signpost people to their website for a good guide on each of the mechanics when they get to end game. I'm fine with it but I can imagine a lot of people trying PoE for the first time, loving the campaign then getting to end game and not having a clue what is going on.
In short the end game new player experience is really really bad and other than pinnacle bosses lacks any challenge and/or removes that challenge so you can't overcome it.

And in closing, for the love of whatever you worship make it so when you get to maps you're given a buff that increases your movement speed when you haven't been in combat recently.