I’m currently making an open-world pvp with @CodedJack and we stumbled upon an issue… our game was too plain…
Take examples like Rust and Ark: Survival Evolved as a reference. What are some essential game mechanics we should include? This can be player based or game mechanic based.
I look forward to your feedback. 
Add an avatar customization experience! This’ll add personality to the game for anyone who plays it.
Hello,
For PvP games, here some suggestions that could probably be used into pvp games
Adding Gems currency to the leaderboard that could be used to purchases important and rare items to fight with,
The player would probably spend more time for Gems and try getting them from something or someone because of its rarity.
Players would probably want a Boss to fight :
An area with random generated boss when defeated with a reward.
Players does not like to get spam killed by someone
That option would be useful to players who would want to play peacefully
That all of my suggestions.
Waru
Disasters that can destroy bases and resources around them, making it to where there isn’t any “OP” places to settle. 
My best suggestions would be:
1. Add interesting forms of movement, sliding, rolling, climbing, the works, but make it make sense
2. Make it impossible to spawn kill, people ABSOLUTELY hate being repeatably spawn killed
3. NPCs or Non-Player Characters are also a wonderful way to add something to your game
4. Add some wacky weapons, or perhaps some easter eggs around the map, a lot of people love the little details even if they seem insignificant to you
5. Customization of any sort is a great way to make it a little more exciting