I hate the ledges that can be jumped too but can't be grabbed, i.e.
>jumping to another building
>easily in range to grab ledge and pull self up
>smacks into it and falls
>HHHHHHHNNNNNNNGGGGGGG
And inconsistant physics, i.e.
>shoots tissue box
>doesn't move and just spawns a decal on the side
>shoots car
>explodes and pieces fly everywhere
>???
(I'm looking at you, Valve, with your silly immobile tables, computers, and unbreakable window glass, drywall, etc)
Also ammo in churches and other places like that is dumb unless it is explained that someone was there to put it there (like HL2: Lost Coast with the Combinified church, it's understandable that there would be ammo there)