Metal Slug has grown to be a legendary title, well-known for its fast action, fluid animation and sense of humour. It's also been ported to just about anything that's able to play games, from the Wii to iPhones.
Thanks to its limited production run, the original Neo Geo version of the game is still very sought after, leading to its heavily inflated price.
When you think of the Nintendo 64, it's unlikely that the Real Time Strategies would be the first genre you'd associate with it. You'd be right too, as StarCraft 64 was one of the only RTS titles to hit the console, and it was far inferior to the original PC version.
The Australian PAL edition is the most valuable one to own at the moment, with copies having been sold for in excess of $500. Even unboxed copies can go for as much as $200.