I know it's completely opposed to the philosophy of this game, but I'd like a server where the game is an utter nightmare in terms of difficulty. Enemies hit like a truck and don't die so easily. You will absolutely die if you go on autopilot and try to wipe boards. Your defense is as important as your offense. I had hoped that reboot would be like this, but I see it's not at all.
Yes, bosses can be extremely hard, but 99% of the game is mobbing, and I'd just prefer that to be a heavy challenge too. It would feel like more of an accomplishment as I level, and would be tons of fun to have a server like this where everyone is in the same boat. I think teamwork would be more encouraged, and rank would be more meaningful.