At least having humans running around gives some illusion of intelligence in the world.
Destiny's AI is broken to non-existant. Enemies aren't smart at all, 100% of any (very little) challenge comes from being a) mobbed by a lot of enemies at once from every direction or b) bosses/sub-bosses who do ridiculous AoE damage (like the tank thing).
Enemies will face the wrong direction, run towards you from too far, randomly take cover or break from cover for no apparent reason, elite enemies (knights, wizards etc.) for the most part simply stand out in the wide open then warp a short distance away after taking damage.
The worst are thralls, an enemy that simply runs at you to melee isn't awful in theory, but they only chase you a hilariously small distance before they will literally stop and walk backwards while facing you. Bungie can't even get the most basic, purposefully braindead AI correct/to play well with the game design.
Would be hilarious if it wasn't so sad. Still I bought the Digital CE after having all these concerns with the beta, so I'm as much a problem as everyone else who bought into the hype.