I know this topic is discussed here frequently, but I figured I'd give my two cents anyway. For context, I mostly play with my friends who are all in the same region, grinding monos together and upping the corruption. Some technical issues and design choices regarding multiplayer really makes it a lesser experience than what it could be, so I hope we could get some love from EHG on the following:

Technical issues

• The party system is overall buggy and unresponsive, invites can take several seconds to arrive or not arrive at all. There's also a significant delay between accepting the invite and actually joining the party.
• Sometimes someone will join the party, but won't be visible as a party member to other members.
• When a player enters the game, it takes several seconds for they to appear as online in the friends list.
• Sometimes in the friends list, it shows that some players are playing an offline character when they're actually not, making it impossible to invite them to a party in this case.
• Sometimes when in monoliths, if a player joins the party and tries to teleport to another player, they'll go to what we call "the limbo", a buggy dark place that appears to be under the map.
• Sometimes the party will get to a bugged state where no one gets XP, enemies in monoliths will die but keep standing with zero health.
• Often times, someone will get an infinite loading screen when trying to teleport to another player, having to quit the game to try again.
• When someone is inside an echo and there are players in the lobby area, they can get hit by things falling off the sky and die.
• When playing in dungeons while in a party, transitioning from one level/floor to another is a problem. Not only it can take several seconds to transition and load, but often times someone will get disconnected while doing so.

The amount of times we have to make everyone leave the game and enter it again just to create a fresh party because of bugs is no joke. This usually fixes it.

Design choices

• The most obvious one: corruption progression is not shared and it's earned only by the player who opened the echo, even though everyone in the party gains and spends their stability when playing. This leaves my friends in a weird position where the only way they can play in high corruption (without grinding it all again themselves), is to wait for me to be online.
• Echo rewards are not the same for everyone. Although we are now all aware of this, when we first started playing it led to a lot of confusion where I would select an echo that had a reward that my friend was looking for, only for his reward to be completely different than mine in the end. This makes target farming echo rewards in a group very inefficient and awkward.
• Some builds can be really flashy or crowded and cause a lot of screen clutter (I'm looking at you, Runemaster). An option to lower the visibility/opacity of friendly minions and spells would be so nice! Also, why do I need to see the health bars of every single minion from my friends? I only care about mine.

I probably forgot some stuff, these are just from the top of my head. Would you add anything else?