This is something I like and need.. there's been many wonderful custom servers but they never last. There will always be those people who play 24/7 and fly through all the content which is no fun because then they have nothing do to and complain non-stop which puts stress on the developers. In my opinion, when playing a custom server, 1 single handed person should not be able to do everything themselves.. there should be tons of HARD bosses, quests that need multiple people, etc.. you should not be able to play a server solo... teamwork is what make it fun, I love teamwork. When having a tank they should actually be USEFUL... same with support vocations. Also, this way 1 single person can't just beat or rush through the server, they will need help from other people in order to progress.
Economies are the best! I love it when servers have a working economy and not just use NPCs for everything. I mean yeah you might sell an item here and there to someone but that's nothing... When a sever has people constantly spamming in trade. Selling, buying, trading all kinds of stuff now that's an economy.. When there is a supply and demand for items.. But if all you do is hunter monsters, sell items to NPCs, buy next weapon from NPC, and so on.. that's no fun lol...economies are really hard to get working, but it's well worth the effort
- Secrets, riddles, puzzles, challenging quests, etc..
This is what makes a server fun and exciting... I'm so tired of seeing all these bland and boring maps, like what the hell, please get creative. I absolutely love it when there are riddles and such to solve. As well as all kinds of secrets, like clicking on a certain stone will open a door something, hidden holes under trees, finding keys that open doors, switches around the map that unlock places, all the containers/corpses placed on the map should be filled with items, could be anything from bones, to a rotten banana peel, or even something valuable like items, gems, equipment etc.. just make the server feel more alive and detailed.. don't make it just about grinding and getting better equips. Make the quests in depth ones... not just go kill 100 of this monster, or go get 25 of this item.. I guess that's alright for tasks, but quests should be detailed, need to make you think, etc..
I could keep on going but I'm to lazy XD