Metroid Blast's multiplayer totally trumps Metroid Prime 2. And likely a whole bunch of other shooters, too.
Metroid Blast, which saw early life as the E3 2011 demo Battle Mii, has three modes: a cooperative horde mode, Ground vs. Air competitive multiplayer, and Ground vs. Ground competitive multiplayer. Ground vs. Ground was not playable, but that's just a standard third-person shooter deathmatch as far as we know.
The other two modes make use of the brilliant asynchronous gameplay and turn it into a fast-paced shooter. The co-op, which was shown off during the North American press conference, pairs up a GamePad player and anywhere from one to four Wii Remote and Nunchuk players. The competitive mode shown pit the GamePad player against anywhere from one to four Wii Remote and Nunchuk players.
On the GamePad, you control Samus' gunship. The controls are very complex, easily the most complex in Nintendo Land. The two analog sticks control horizontal and vertical movement, while the GamePad's gyroscope controls your view of the area and your reticule. The shoulder buttons let you zoom in, fire your weapon, or charge up a missile. It's all easy to understand, but difficult to put into practice. It is a brand new control method, and thus, there is a learning curve. However, once you get past that learning curve, it is awesome. Having basically three ways to tweak the control of your ship is fantastic, and while the Wii Remote and Nunchuk players had a strong advantage at the beginning of the day, as myself and other players got accustomed to the GamePad controls, it became very even.
The Wii Remote and Nunchuk players play as Miis in Samus suits, who control like a third-person shooter on Wii. You move with the Nunchuk's analog stick, and point at the screen to aim. By holding the A button, you can move with the analog stick while also using the pointer to aim. It feels very nice. Additionally, these characters can roll into a morph ball by holding the Z button, dodge by shaking the Wii Remote, and charge up missiles by holding down the B button, which is also used for firing regular shots. They can even grapple at certain points to either gain ground, escape a hairy situation, or get a better vantage point.
The co-op mode was a lot of fun, as you fought off waves of enemies. There are a whole variety of levels (at least 16 from what I've heard), and they are all very replayable with friends. You can even team up by having the Samus players grapple onto the ship. Teamwork is required, especially as it gets harder. Each player has three hearts, and if you lose one by being hit, you can regain it by collecting one on the playfield. Unfortunately, these hearts can be shot or exploded, rendering them useless.
Also in this mode, the ship can be shot down, making the GamePad player have to run around, totally defenseless, searching for a heart. I ran into this one time, and almost wanted to slap my compatriots as they kept on destroying hearts I was just about to collect.
The competitive mode is more like the other Nintendo Land games that make the GamePad player play against the other players, who have to team up to win. The ship has the equivalent hearts of all the players, so if you have four Wii Remote players with three hearts each, then the ship would have 12 hearts. There seem to be several arenas with their own intricacies for this mode, though only one was shown off. This is another example of how Nintendo Land takes something familiar and makes it new and fresh. We've all played deathmatch shooter games before, but adding in the ship makes it a whole new experience.
Metroid Blast might be the most "hardcore" game on Nintendo Land. It is incredibly fun, and with the lovely Metroid references, including some sweet musical remixes, it should be a blast (sorry) for a lot of players.
Note: In case you're curious, the image below is what the Ground vs. Ground deathmatch mode looks like. It appears that GamePad will show a dynamic view of the match.