Neo Geo games in general are pretty rare because they were expensive to make and this caused many titles to be released in low quantities. There are however some games that are more rare than any others. The prices can go crazy high (in the thousands), so a Neo Geo collector would need to be very serious about their buys. Do your research and find the deals! Most of the games listed here today would all fall into the top 15 (maybe top 20) rarest Neo Geo games. Many of the prices these are going for are great deals.
Metal Slug Complete Series (MVS) – cartridges only