One of the things that you notice pretty quickly if you play the PS2 game "Baldur's Gate: Dark Alliance" is that the plot is not so much full of holes as it is like netting. The plot, as revealed by the exposition, contradicts itself in some places and fails to hang together utterly in other places. This is largely independent of the game which is played, though, because since there are no decision points in the game, the story is optional.
The believability that one really notices, especially when you're playing the game a second time, is the way that all of the boards are impossible. There is a ridiculous density of monsters (and other bad guys) who are supposed to be just hanging out, going about their day. It would be one thing if they were on patrol, waiting for you. But no, they just all hang out about 25 feet apart from each other in a near grid pattern, with no food sources in sight, and no sources of entertainment, either. They just stand around, looking at nothing, all day long.
Worse, they all have terrible eyesight and hearing. You kill one, then the one 25' away doesn't notice the pitched battle going on next to it, so it just stands there rather than joining. And all of them are this bad at noticing loud explosions, no less (even when those explosions are caused by three 5 gallon barrels of black powder).
It's a small thing, and of course the justification is game play — nothing could possibly be even slightly comparable in importance to game play! — which is the creative license of games. I wish that it would occur to some people that if you destroy all believability, the game play is a lot less exciting.