A "proper review" of a Neo Geo ROM requires a significant technical correction: Metal Slug 6 was never officially released for the Neo Geo.
When searching for "high quality" downloads, keep these tips in mind: new download neo geo roms metal slug 6 rom high quality
was the first main entry in the series to move away from SNK's aging Neo Geo hardware. It was developed for the arcade platform. A "proper review" of a Neo Geo ROM