The Descented is a survival SMP with a tougher twist. You start in the Nether, mobs are stronger, and enchants have been improved, so progression is a bit more challenging than your usual survival world.
Simple Voice Chat is enabled, so talking and teaming up with other players is part of the experience. The server also keeps things open to player suggestions, as long as they make sense, so the world can grow with the community.
There's also a possible world reset in the future if enough people want a fresh start, so it's the kind of server where the direction can change with what players are actually asking for.