OK, people have to stop saying Metroid Prime 2 did badly. Yes it didn't sell as good as the first but it still sold well.
Metroid Prime 2 Sales
North America - 800,000
Japan - 70,000
Europe - 370,000
Total - 1.24 million
The reason Prime 2 didn't sell as well as Nintendo hoped was because of bad marketing, coming out the same time as Halo 2, and the biggest reason is the fact that the Gamecube was on it's death bed back in the fall of 2004.
The first Metroid Prime was released back in the fall of 2002 when the Gamecube was still considered alive by most people. If you look at the sales back then you'll see that Gamecube games were putting up good numbers and since Prime was the Gamecubes flagship title for the holiday it was the must have item for Gamecube owners. Jump ahead 2 years and the Gamecube was in bad shape. Third Parties had all completly abandoned the system and the media only talked about the PS2 and the X-Box, and so the Gamecube was all but forgotten by the average gamer. So the only audience left for Prime 2 was the remaining hardcore Nintendo fans and that was it.
The fact that Prime 3 will be coming out now when the Wii is insanely popular I say is going to give it really good sales, but it'll never be a huge hit. The Metroid franchise just isn't the type of series that alot of people play. Yes it has a good sized loyal hardcore fanbase but to the average person, it's just not their thing. I think it comes down to how you really have to think in Metroid games to figure your way through the world is what makes people back off.
Plus people also have to realize that the Metroid franchise has never been insanely popular. Look at the numbers for the other Metroid games and you'll see the series has never really had huge mass market appeal.
Metroid
North America - 1.35 million
Japan - 1.04 million
Europe - 340,000
Total - 2.73 million
Metroid II: Return of Samus
North America - 860,000
Japan - 520,000
Europe - 340,000
Total - 1.72 million
Super Metroid
North America - 580,000
Japan - 710,000
Europe - 130,000
Total - 1.42 million
Metroid Fusion
North America - 1.08 million
Japan - 180,000
Europe - 290,000
Total - 1.55 million
Metroid Prime
North America - 1.92 million
Japan - 120,000
Europe -730,000
Total - 2.77 million
I already posted Prime 2's numbers, plus Zero Mission and Hunters both never passed the million mark so VGcharts doesn't have numbers for them.