If there are only a few and relatively small obstacles on the map you might get away with something like this:
Resetting the velocity to 0 and then using a greater force simply towards the player's position is probably enough (especially if your enemies are zombies or something on the dumber side). Getting rid of pathfinding will mean better performance and enemies can still "push around" small obstacles; using immovable physics objects with circle collision masks for trees and such is probably a good idea.