Charon121: There was a thread not long ago called "little things you hate in games". This one is about the big things, or fundamental game mechanics that you can't stomach, but that everyone around you adores. I'll start with a few things:
Dungeons: the staple of every RPG and most action adventures since the beginnings of computer games. Labyrinthine corridors with monotone textures filled with illogically placed loot and a nonsense ecosystem of critters. For some odd reason, torches are always lit, and foodstuffs are never rotten. They can take many forms, but most commonly that of a dreary castle dungeon, absurdly spacious sewers, swamp where your movement is restricted, forest with conveniently cut passages going through it, etc. Sometimes developers get creative, but even if the dungeon is a massive tree bough, it's always the same labyrinthine corridors, creatures that sit tight waiting for you to stumble upon them, and valuable stuff left around. I'll take a logical overworld map or city setting anytime over dungeons, which I consider to be lazy design. Huge sprawling dungeons are even worse because they never seem to end.
Haha, this one tickles me. I found it amusing in games like Darkstone when there's a creature just sitting in a room behind a locked door. It kind of gets you thinking, isn't my character little more than a monster to them, going into their places of living, smashing through their barricades, killing everyone there, and taking everything that isn't nailed down? Obviously those 'dungeons' are actually fortresses designed by their inhabitants to protect them from pillaging 'heroes'.