This game is somewhat of a double-edged sword.
If you have a friend (or enemy) who is in the room with you, this game is great. Otherwise, you probably shouldn't get it.
The game plays like an elaborate dance; two players fighting for the honour of being consumed by the titular serpent- the Nidhogg. The controls are simple: one button jabs your sword, one button makes you jump. The real beauty is how the mechanics blend together. Swords can be moved up and down to reach a jumping or ducking enemy. Swords at the same height will clash, and can block the opposing player's attacks. Swords can also be knocked out of a players hand by some particularly crafty swordplay. Jousting with your sword fully raised throws your sword through the air, which is hard to dodge, but leaves you without your best weapon. Thrusting in midair results in a divekick, a techniquie used to relieve the enemy of their weapon (that is, if you don't impale yourself on their weapon first).
The result is an EXTREMELY intense sword battle. Matches can last for seconds, others can last for half of an hour or more. The ducking and dodging and jumping and running blends brilliantly with the game's glitch-art style and kickass music. You can play this before the start of a lecture. You can play this at a party, with a tournament of eight players. You can use it as a substitute for rock-paper-scissors in decision-making situations. It's become one of my go-to games when friends are over (see also: touhou 9).
However, this only applies if you have real-life friends. Sure, the game has online play, but it's horribly laggy and bugged, with no sign of a fix. The lag ruins the crucial fast-paced action of the game and usually results in the host player winning. Because of this, you'll be very lucky to actually find anyone through the matchmaking service. The single-player mode is basically multiplayer but against a series of bots, which each have distinct playstyles and weaknesses. It's very much like playing against real players, but nowhere near as fun as having friends to play with in the same room. Additionally, the price is VERY steep for what the contents of the game are: only four (admittedly BEAUTIFUL) levels.
Overall: One of the best local multiplayer games that exist. If you have real friends that can come over and play: get this game ...but get it during a sale. If you have no friends: sorry, this game isn't for you. Go out and make some friends instead!