If you haven't been playing, you totally should be.
Spiral Knights is a free-to-play action-RPG MMO created by Three Rings, best known for the game Puzzle Pirates (RIP Salty Mouthfuls.) Sega bought Three Rings, and the rest is history. In the game, the player controls a knight of the Spiral Knights order, which has crash-landed on the mysterious planet Cradle. Knights collectively explore the Clockworks, the mechanized, constantly reorganizing dungeon that fills the planet's interior. The knights equip armor and weapons to aid them in their battles against the monsters inhabiting the Clockworks. When they are not exploring, knights trade with each other and with vendors, in order to improve their equipment. Despite the many references to both the Clockworks AND Knights, the game sadly has no relation to the Clockwork Knight franchise.
I assure you that the plot really does not matter.
Unlike traditional MMORPGs, Spiral Knights is a lot more casual. A lot. This isn't PSO2 by any stretch of the imagination. You have a variety of weapons—a sword, a gun and a bomb—and you traverse the world of the Clockworks, leveling up, getting new gear, and bullshitting around with cool people. Spiral Knights is to MMORPGs what bowling is to sports: not all that serious but still pretty fun, especially when you've had a beer or two. It's moderately challenging, but nothing you have to invest large amounts of time into to become a good player.
You should play Spiral Knights with the Retro crew! Our official guild is the Clock Ork Knights (thanks, MainMemory!) It's a great time-waster and it's free.