Metal Gear Rising: Revengeance isn't just a completely rad action game, it's a great way to test the waters for further Metal Gear spin-offs. According to a VG247 interview with series mastermind Hideo Kojima, it looks like that could be a possibility, and he even has a vague idea of one such spin-off.
"I think Rising was a special case. In the future I may make other games, maybe featuring The Boss as a main character," Kojima said. "That's something I want to make personally, but as far as a series of spin-offs—there may be another Rising in the future, but it's not something I want to make a habit of."
A spin-off centered on The Boss would definitely be great. Are there any other Metal Gear Solid characters you'd like to see get their own game?