Do you have to kill rats?
Yes. Lots. The only dungeon that I went into was infested and the security turrets seemed not to notice them, while it was very aggressive towards me every time I looked at the corner of the corridor. .
Does the AI suck as much as it appears in the gameplay videos?
Yes, unfortunately, itís one of the main faults of the full version of Fallout 3. The mobs are totally stupid, with NPCs that flee in the direction of their aggressors, enemies that find themselves running on the spot, blocked by a too-low platform ( enabling me to re-arrange their faces during combat), rats that charge you so close as to bump into you then jumping up and down in a vain attempt to cause you harm. It is the one point that Bethesda should be taken to task over.