-nope-
1. The competition. Baltop, Island Top, McMMO etc.
2. On Survival I like having the classic game but with Economy and McMMO etc. and on SkyBlock I just like the whole challenge and then things becoming more and more easy after playing for a while.
3. Many things. Some of the large ones for me would be not being able to do /baltop or balances of others (many small servers assume you can see others' balances with just 'essentials.balance' but you need 'essentials.balance.others' in Pex or whatever you use).
Also PvP everywhere except spawn when you're on a Survival or SkyBlock Server.
Also try to get your server popularity relatively even throughout the day (e.g. One SkyBlock server I know has about 100 players at one point in the day and about 10 at another time of the day.) This annoys me because I have to get on at a certain time of the day or I'll be basically alone.
4. There needs to be a large server shop and something like individual player warps and player shops in my opinion.
Hope this helped you! I'm happy to say more if you want to ask more questions!
~Bear