Certain quests are impossible to complete the moment they are given because you can't even hit the enemy you were assigned to kill. With some quests the only way you can kill a target is to backstab, and even assuming you aren't spotted backstab will fail to do enough damage three out of four times. At that point you're stuck with an enemy that can kill you in three hits and regenerates faster than you can damage it. The best term for this is 'realistic' since in real life nothing is guaranteed either, but this can be a turn off for some. Other than this the levels are very well designed with interesting layouts, logical results from your actions, and great looking scenery.
Quests are sometimes a bit contrived but make sense and are fun to achieve.
Evil Islands has the best pathfinding and reaction AI I've seen. You can click anywhere on the map and your characters will take the best route to get there. If they can't get there, say a door is in the way, they'll walk over to the door. For example, if your attack value is much higher than your enemies' defense value you can target the head for extra damage. If your enemy does a lot of damage to you but has a low defense you can target its arms to make it swing less often.