Many things. Three worst offenders:
1. Mixing real life cash with game content. I'll go to a store and buy a game, I don't want to see anything referring to your business plans in the game.
2. Health bars. Why is it that firing a shotgun at someone has no effect on them except lowering their health bar by some points? A person with 1 health is just as able as a person with 100 health. Why?
3. Game designers ought to pay more attention that looks of things are in harmony with abilities of said things. Mario series are good examples of games that don't strive to be graphically realistic, but feature logical design decisions. If you see a monster made of rock, you can't kill it (makes sense?). Fiery monsters can be doused with water, not by shooting them repeatedly with shotgun draining their healthbar...