Core Issues to Fix (High Priority) at my best speculations and gameplay so far.

Performance & Lag Spikes
Heavy particle effects + lots of enemies = FPS drops
Worse in party play or high-density fights

Add advanced graphics toggles (disable specific effects like shadows, spell clutter, ground effects more advanced options to make them even better and optimized)
Optional “low-clarity combat mode” for smoother gameplay
Better CPU/GPU optimization during peak combat

Party & Quest Sync Bugs

One player gets reward, others don’t
Players forced to relog or leave party

Suggestion:

Ensure shared quest progression and rewards
Add failsafe resync button (instead of restarting game)
Clear UI feedback: who received what and why in other words Quest progression in parties feels inconsistent and sometimes forces players to reset instances. This breaks co-op flow and should be more reliable and transparent.

Loot System & Filters

Not everyone knows about external tools
Early game = too much clutter
Suggestion:

Built-in loot filter system (official UI)
Starter presets (Beginner / Strict / Endgame)
Better item readability on ground or similar to poe filter readability.
While community filters are great, integrating an in-game system would improve accessibility for newer players

Combat Clarity

This ties into lag but is also gameplay.

Too many effects = hard to see what kills you
Visual overload in late fights

Suggestion:

Tone down visual noise
Improve enemy telegraphing
Add ‘danger highlight’ system for lethal mechanics

Content & Long-Term Ideas

More map variety
Unique mechanics per region
Seasonal or rotating map modifiers
Expand atlas-style systems or the system for atlas specifically make it more acessable for new players aswell once players reach end game.

One of the biggest strengths of Path of Exile 2 should be freedom.

Suggestion:

Easier respec early game which already kinda has been added to the game which is good job yet costs some gold ofcourse.
More skill experimentation tools
Training dummy or DPS testing area

Quality-of-Life Improvements

Suggestion:

Built-in guides/tutorial overlays
Explain stats, crafting, scaling better, for veterans easily can be turned off from settings.