Open PvP mode requires some adjustments with level design(which is normally theme/PvE oriented)
Usually levels should not leave advantage to specific class, allowing one side to mass only one class/specialization and dominate the environment.
Mass PvP areas should not contain many particles or high-impact graphics.

Bad designs:
1. Large open areas with little obstacles: usually should be avoided, this leads to most ranged attackers having an edge.
2. Closed mazes with confined/narrow passages: this benefits stealth/melee ambush mechanics and should be avoided too(it confines ranged attacks).

Good designs:
1.Open areas intersected with closed areas(walls) and many obstacles:
provides a mixed environment with tactical threats.
Long range attacks must have a clear line of sight: balanced by obstacles and boundaries.
Melee/stealth/ambush attacks are balanced by flexible movement options.
2.Mazes with wide passages, multiple exits and few obstacles: ideal for close range PvP and good for medium range. Long range attacks are confined to medium range.