Excellent idea, Datadog! I do have one request, however. That we change the title to "Cliches in Games." That way it'd include all types, since every genre has a ton of cliches to mention.
Since I can't think of any Adventure Game cliches (aside from the ones already stated), I'll rant on about First-Person Shooters and Role-Playing Games.
First-Person Shooters
1. If something moves, kill it.
2. Your teammates are only there to give the enemy another object to shoot.
3. If your teammates are AI-controlled, they'll run directly into enemy fire, run into walls and over mines, eventually getting themselves killed. Sometimes this necessitates a restart.
4. If your teammates are real players, they'll run directly into enemy fire, run into walls and over mines, eventually getting themselves killed. Inevitably, they'll blame you for this and at the next available opportunity, kill you if team damage is on.
5. If you kill someone online with a shot took some degree of skill, the player who died will yell out that you're a "hacker" or "using cheats/exploits."
6. There's no such thing as "friendly fire." If you're in the way of a teammate's shot, you will be taken down along with the enemy. The only time this isn't true is if team damage is off or the firing player (and potentially the entire team) will be penalized for shooting teammates.
7. If audio taunts are available, they will be spammed over and over again during the game.
8. If vehicles are available, players will drive off cliffs, over mines, flip over and get stuck somewhere they can't move. If the vehicle in question is a plane, players will crash on the runway, crash immediately upon take-off or just crash after the next available opportunity shows itself. If the vehicle is a helicopter, the player will be lucky to even get it off the ground -- usually they'll crash within seconds of taking the controls.
9. Players will find the most powerful weapon and/or effective class of character and use only those during the game. It's rare to see people choosing classes that might actually help their team in a support role (such as a medic or engineer).
10. The player will most likely find themselves in World War II. After all, who gets tired of storming Normandy Beach?
Role-Playing Games
1. The hero will start with few relatively decent skills, lack weapons beyond a short sword and buckler, and wear armor that has the same protective qualities as a sheet of paper. Even if the game is a sequel or an expansion, somehow the hero will still lose his skills and weaponry.
2. The main character will usually be a young man or woman (a teenager if it's a console game) who never wanted to be a hero, but is thrust into a life of adventure.
3. In the start of the game, physically-oriented characters are far better off than spellcasters. As the game progresses, those who rely on armor and weapons will have to constantly upgrade while magic users become increasingly powerful (sometimes to the point of achieving demi-god status).
4. Expect to take part in numerous "FedEx" quests and simply accept that backtracking is a way of life. Side quests are usually optional, but if the hero doesn't take them, he'll miss out on some items, skills, spells and experience.
5. The villain is described as an "all-powerful being," yet the best he can do is muster up some rats and rock-tossing octopi at the start of the game. In addition, animals --unless specified -- will always be aggressive and attack the player.
6. If there's a tavern, there will be rats to kill in the basement.
7. Skills, abilities, weapons, armor and magic will be renamed if the game is science-fiction. However, the basic idea will remain the same (i.e. lightsabers instead of swords, guns instead of bows/crossbows, implants instead of magical items, the Force instead of magic, etc).
8. The hero has to talk to everyone. If he doesn't, he may miss the old crippled man in the alley who just happens to have a piece of the "magical glass orb" or "doomsday device" after he won it in a poker match.
9. If you can name your own characters, NPCs will refer to you by whatever name you enter, even if means stating your whole name every time they speak to you.
10. There are never enough options when creating a character and in the end, your character will look like a dork (or a dorkette, whichever the case may be). If you do somehow create a character you like, at some point in the game, you'll want to change the character somehow (i.e. hair style, eyes, facial structure, etc).