Spiral knights is an MMORPG (which stands for Massively Multiplayer Online Role Playing Game). This game was developed by Three Rings Studios, a componay owned by SEGA.
There is no clear objective to the game although you can technically get to the end of the rank system. Most players generally regard reaching the end of the rank system as half the game.
The game is entirely F2P (free to play) but does give large advantages to paying players. Paying money can get you gear faster as well as cosmetics. Almost all gear is available to the F2P community
Pros and Cons of Spiral Knights: