Beat the game just now, pretty great.
The AI on both sides is pretty silly sometimes. Not too long after Ellie joined me, we were in an area with some normal human enemies. Stalking around, killing 'em silently, everything is going well. One of them begins to walk by in front of whatever I'm using for cover, so I'm waiting for him to come around the side where I can pop out and grab him...
..and then behind me, Ellie yells "HEY, FUCKER!" and half a second later a brick came flying over Joel's head and hit the guy right in the face while his buddies elsewhere started to come running.
It was dumb but I must admit I laughed my ass off.