I think the definition of 'gamey' really depends on why a person plays a given game in the first place.
Allow me to posit a hypothetical game player, one who plays a given game because they find the 'game universe' to be compelling, for varying reasons. Perhaps they enjoy science fiction-inspired settings, or maybe they have personal interest in the historical perspectives offered by a game, or maybe the fantasy elements really appeal to our hypothetical game player. This type of player will often try to stay true to a particular style of play that they feel is consistent with the spirit in which the game is intended, at least as they perceive it. This is how they enjoy the game, by trying to stay 'in character', as it where.
Let's say another hypothetical player-type is also attracted to the fictional universe in question, but maybe not to the same degree. This person gets greater enjoyment out of the strategic challenges, or empire building, and doesn't balk at the micromanagement required to get the most out of their position in the game. While this player may also have been attracted to the game by the coolness of the science fiction/fantasy/historical/etc theme of the game, what they really enjoy is the down and dirty nuts and bolts of the game system, and the challenge of outplaying their rivals and winning the game. The setting is just an added bonus, making the micromanagement tolerable. After all, who would play SEIV if all the graphics where removed, and it was distilled down to a huge spreadsheet? Not too many people, I think.
Generally speaking, these two types of game players will get along just fine. But where their philosophies overlap there is a bit of a gray area. This gray area is where the term 'gamey' comes into play. A Nuts and Bolts (NaB) player may see absolutely nothing wrong with a particular tactic (I won't get specific because it's open to interpretation), since this tactic is clearly allowed by the rules and doesn't involve obviously nefarious methods like hacking the game/exploiting bugs in the software, etc. The Spirit of the Game (SoG) player, however, may view such a tactic as 'gamey', as it clearly (to them) goes against the implied spirit of the game universe, although it is technically allowed (usually by the limitations of programming a simulation of a huge universe). (By the way, I hope no one objects to my terms, I'm not trying to stereotype anyone.) The SoG's argument would be along the lines of "Your race would never do (insert tactic here), you are playing unrealistically and exploiting the limitations of the medium!" while the NaB's response might be "What are you talking about? I'm not breaking any rules, and I can't believe you are being so anal. It's just a game!" or something to that effect.
Most times, of course, arguments like this never arise, but some tactics eventually come to be viewed with increasing suspicion over time, and will occasionally spawn the 'gamey' debate. Neither side is right or wrong, of course, because they each have their own motivations for playing the game. In a game like chess, which is already distilled down to its tactical essence, this type of debate would never arise. Can you imagine: "Why is your king hiding! That would never happen in the Middle Ages, kings always led their armies into battle!!"
Anyway, that's my rambling take on the 'gamey' term. I hope it made at least a little sense.
