Gauntlet Legends
Like the last post, this hearkens back to a simpler, and therefore much less convenient time. Before Mass Multiplayer, there was direct connection to your friend's IP address. Before that? well, you actually had to go to someone's house and pick up a controller that was (god forbid) wired to the actual machine.
Getting to a friends house wasn't terrible, but it was pretty hard to find a good game where 3 or 4 people could play together. Most of the consoles provided only 2 controllers, and when it jumped up to 4, the games were focused on competitive play. As fun as it was to shoot your friends with a PP7, I yearned for a game that you could play WITH your friends and progress your characters together.
The 4-player RPG was pretty much non-existent until Gauntlet Legends. I had Gauntlet 2 on the NES which I would play with my cousin, but that game was a pretty bare bones action RPG that I only played once and a while. When I saw Gauntlet legends at the arcade, I was blown away by how much action they packed into the game, and I had a blast plowing through the endless hordes of bad guys. When I later rented it for my N64, Gauntlet Legends was absolutely one of the best all-night party games of the day and even now I'd be up for going to a friends to play this gem again.