So, here we go, some ideas that might be useful.
Grind Quest
I wrote this in one of my posts, but I think it might be better to be here. Grinding becomes really dull after some point, a nice solution would be a "grind quest. After every 100 mob you should get xp cards accurate to the mobs level. The xp cards number would be increased by the number of party members. That would encourage players to play together, also help the grind mechanics and feels less pointless to grind. Thou, on higher levels these cards should give decent xp.
Pings
Would be nice to ping to others on minimap, so we can navigate faster to our goal.
Port to each other
Might should be a guild perk or party skill. In every 10 minute or so you could summon your party to you, or they can summon you. Easier navigation and better coordination.
Customization
Please, just do something about it. Everybody loves to play a character which can reflect his/her personality. While it was ok in Ragnarok, since it’s an old game, it’s pretty dissapointing to have just a few option to make our characters unique. Since items are not showing on our toons (just the hats) you have to give us much more options. It’s pretty sad when you see the same character running around everywhere.
“Dead branch”
If you played Ragnarok, you remember this. Something like that would be very fun.

", rather than "Awww, now I need 100 more till I get another card
".