Fallout 3, Oblivion & Mass Effect
Unfinished aspects! Let me elaborate, they try to put a lot of stuff in there, so mush so that they can't finish it, or elaborate on it.
Several dungeons in Oblivion, one I can't remember it's name, had translated tablets about a flood, there was nothing special in there, at all! What a waste, especially after reading the tablets and getting worked up.
The Sat-Com arrays, they seem to do nothing, you can't reactivate them, you can't do so much with it it's really annoying.
The giant skull in Mass Effect, *deep breath* WHAT IS IT FROM!?! oh and how unsatisfying was the damned floating prothean orb!