Depending on the genre of game you’re playing, how you perceive an AI enemy can differ a lot. The Player-Enemy Relationship Diagram places player-enemy relationships into three categories.

Hate

Hate, often referred to as a “strong word”, is perfect for defining the relationship that players have with the enemies that fit into this category. We have all experienced that moment when we were slain by an enemy resulting in a smashed controller or the exclamation of a curse. The level of emotion that a “Hateable” enemy provokes is reliant on the player’s endurance and their immersion into the game, but these hateable enemies do share characteristics.

Unexpected Difficulty Spike
One of the most obvious traits is the extreme offset in difficulty. In an easy-to-manageable level, the introduction of a tough boss-type monster can make the player feel unskilled and frustrated. After a player's conditioning is broken, every moment/death needed to recalibrate contributes to rage.
Omni-present
Some games will make you feel like your a fish a in a barrel. No matter how many different angles you approach a fight, you'll end up with a similar fail state over and over again. An enemy that seems omni-present chips away at a player’s patience to the point where same mistakes are repeated.
Cathartic Relief
Video games are the only entertainment medium that can make you feel accomplished. It’s a cathartic feeling when a player destroys an enemy that had become the virtual embodiment of their unhappiness. That sough after “Yes! I did it!” moment in a game is suppled by those enemies you hate.

Play

Playful enemies are incompetent at their fictional jobs. They are like stormtroopers or henchmen, in that they have the innate inability of being worthy opposition. The only time this category of enemy should manage to defeat the player is when the player disrespects their player-enemy relationship bounds and plays foolishly.

Poor Planning
An encounter with this type of enemy can range from fair to unfair (for them). This is usually accomplished by giving them tactics that just don’t seem to make sense. Some examples of this are rappelling in while in plain sight of the player and deciding to storm the player AFTER they secured the turret. These strategies are immersion-breakingly stupid, but player enjoyment is put above all else for these enemies.
Flawed
A playful enemy is designed to have moments of human imperfection. He/she will drop a grenade by accident or shoot the explosive barrel that is placed right next to them. It's an emergent display of ineptitude that signals to the player that a deadly fight is actually filled with levity.
Sportsmanlike
Sportsmanship is least expected in a fictional fight, but it is a defining quality of a playful enemy. These enemies have a special set of rules of engagement that ensure the player's enjoyment. The star of the game is the player, and they are to be treated as so. If the player is behind cover; do not simply run past it. If the player is running, miss more often. The price of an enjoyable play experience is often the effectiveness of an enemy.

Defend

With the emergence of the zombie sub-genre in games, the “defend” category is quickly getting populated. The enemies that fit this category simply react to the player. Narratively speaking, these enemies are the ones being antagonized by the player. It is almost inaccurate to define these AI as enemies, but either way they still have a relationship with the player that follows a set of guidelines.

Provokable
These enemies only technically becomes an opposing force when the player triggers them to do so. They are provoked into attack and the player must defend themselves against this newly formed enemy.
Numbers
Because these enemies are not proactive in defeating the player, they can be grouped in enormous numbers. Their size makes them a threat more so than their ability.
Obstructive
This is a “Defend” enemy's defining characteristic, they are time sinks. These enemies are literally just in the way. It is beneficial to avoid these enemies entirely, which is the base of their player-enemy relationship.