Are we talking Metroid Prime?

While it's is true that sales don't encessarily equal quality, it is possible for a game to be good and get good sales.  Halo is an example of this. 

Your joke similitude doesn't hold for a simple reason: sales don't equate to the enjoyment the buyers had from a game, even if you were to take that as a candidate measure of quality. Most game sales happen without the buyer having tried the game first, thus the satisfaction with the product is statistically unknown. Let alone things like immediate satisfaction versus long-term satisfaction, or value perception a posteriori. None of which applies to a joke.

Some games are cult hits even with poor sales because the little audience they gathered is very vocal about their perceived quality. Others sell well over time because of word of mouth which once again is rooted in user satisfaction. And others sell well but are rubbish. Maybe well-marketed, maybe sporting some popular icon, maybe appealing for people who don't look for much quality, and yet still rubbish.

Just as a fever might make you perform blood tests looking for an infection, but might end up being caused by something else entirely, so sales can suggest that there's the chance of great quality, which deserves better examination. But there's no strict correlation between the symptom and a single possible cause.

Very well said.

While I agree that there ARE cases of unsatisfied customers, (obviously), I think you seriously underestimate the power of word of mouth. 

Wii Music would be a good example. Nintendo clearly expected it to be the next Wii Fit, and it was marketed as such. Yet, people decided that it isn't good enough to keep playing with it every day, telling about it to everyone, etc., as they did with Wii Fit. Maybe it was the content, the gameplay, the theme, I don't know. 

A contrary example would be The Sims, that was a minor project at Maxis, with almost zero expectations, after the team got run out of ideas with a dozen mediocre "Sim" games. But for some reason, it became the best selling PC game ever.

Of course, saying that a cult classic is a bad game because only a small minority of 100 million gamers bought it, would be like saying that The Sims is bad because only a small minority of Earth's population bought it. It doesn't matter. The rest is a not the market. Its the same as what I said about comparing genres. 

For example, The Path is full of deep symbolism. You could say, that even though it only sold a few thousand, it did remarkably well for a game in the tiny "deep symbolism genre", and its market.

ps.: "people who don't look for much quality" is nonsense, of course everyone is looking for some sort of quality, as "quality" basically means "good", maybe just from different perspectives. 

^
Still, word of mouth bringing people over the threshold of buying or watching or reading something doesn't indicate that if you took a sample of random people and showed them the product, they would judge it positively. It only indicates a vocal reaction, which is also common to fads, fashions, urban legends and conspiracy theories. If a meme spreads, it's because it is fit to its goal of spreading, not because it's particularly true, deep or meaningful.

Plus, by arbitrarily redefining markets, you deprive the sales of any power of indicating quality because you break comparison. The Path did well for a game in the "deep symbolism genre" compared to what else? And let's say that there's another game that sold worse because it was not reviewed on destructoid. Did it sell well in the "deep symbolistic game not reviewed on destructoid" subcategory? Maybe relatively better than The Path in its genre?

Going back to the OP: are KZ2's sales indicative that it appeals a randomly chosen "virgin" gamer less than Halo 3, or did it sell very well in the "not very arcade-y console FPSs with no estabilished prior community" market sector? While I call them mixed and intertwined causes for sales besides intrinsic qualities of the product, you're quite fuzzy in what you sweep under the carpet of market subdivision and what not.

And btw: "people who don't look for much quality" is a very real case. Just as many DVDs are quickly grabbed from the shelves with the goal of keeping the kids busy while you have dinner with friends, there are games that are bought with no real regard for its quality. "I only want something the kids can play next friday at my daughter's birthday party" has been said to clerks all over the world uncountable times.

That's very true.  Parents buying video games for their children are the perfect example.  For the most part their objective is to buy games for their kids to keep them busy or as gifts during holidays and special occasions.  I highly doubt they do extensive research on the quality of the games they purchase. 

http://www.thefreedictionary.com/hilarious

Yeah well i enjoy most games that sell well, but that's just me.

You need to add a subscript to this topic:

Review scores are not always indicative of a game's quality.