Today, I'd like to spend a few words on what makes a game rare.
In my reviews, I try to rate the rarity factor using a scale that roughly goes from slight / uncommon to very hard to find. This scale is based on a series of elements such as the price, the production run, the desirability and the frequency with which the game shows up on ebay, in forums and in specialized shops.
Some confusion may sometimes arise when a game is particularly sought after and it sells for very high prices although it is not technically rare.
A fitting example of this kind of game would be Dracula X on PCE which is not a rare game in itself but it sells for high prices because there are legions of people that heard about it and it has been widely publicized as being the lost Castlevania masterpiece by the specialized press. Also, it is generally regarded as a good starting point for people who want to get into retro.
By the same token, other games that are objectively rare because of a low production run might just sell for a fraction of Dracula X (that's if they sell at all). In particular, I am thinking of games such as the hugely hyped Circus Lido (which is rare but fairly average as a game).
It follows that in my reviews, a game to be considered rare must meet a certain number of requirements including how good the game actually is. Moreover, I have observed that action games (in particular shooters, fighting games, platform games etc) tend to enhance the desirability factor as opposed as heavy text Japanese games such as RPGs, adventure games, dating sims etc with the notable exception of US / Euro versions of RPGs (because of the absence of the language barrier).
Another interesting point is that games inspired by popular licenses (such as D&D on Saturn for instance) often drive the price up. Some other times, games based on popular anime / manga productions will also be sought after but only for a set time period. When the series starts losing its appeal among the fan base, prices will often drop drastically as the success of the game was linked to a temporary “craze”. So to define a game's rarity , I factor in the following criteria:
Desirability: is the game any good? Are there any language barriers? Is it supported by a popular license?
Price: how much does it sell for on average? In what overall condition the item is?
Production Run: how many copies were produced?
Frequency: with what frequency it shows up on the market?
I hope this might clear up some ambiguities or perplexities that might arise when you don't agree with my rarity classification.