Prime sold 2.82 million according to this website and the original Metroid sold 2.73 million.  I also think the Super Metroid numbers may be off (I remember seeing a higher number somewhere else.)

Ok then, I stand corrected ^^ But if you average the numbers we should get like 1.5-2m... I really wish it was more of a system seller!

I can't find numbers that say that Super Metroid sold more then 1.7, but I swore I saw that it was around 2.1....guess I was wrong.  I was going to write that it was sad that Super Metroid was outsold by Castlevania: Symphony of the Night (which is one of my favorite games of all time, but one that seriously stole a lot of it's playstyle from Super Metroid) but SotN only sold 1.27 million according to this site!  The fact that Super Metroid and Symphony of the Night didnt't combine for 4 million sales on thier initial releases makes me a little sad.

Yeah, Metroid has never been one of Nintendo's biggest selleers, and I would not be surprised to see Pikmin surpass it.  It has, however, always been one of it's more important franchises.  It is different enough from other Nintendo games that Nintendo can point at it and say "See, we do that type of gaming too," it is very critically acclamied, and the series is  influential enough that it has a genre named after it.

I do think that there is great potential in the Metroid franchise, but it never seems to be able to move big numbers... And can any metroid game actually be better than those made by Retro? If those games didn't do more than 2.8m it's hard to see any Metroid game doing better!

Quite frankly, Metroid has become redundant these days. There simply is no big demand for games like Metroid Prime since online gaming became the norm for FPS's, and all new and old Metroid fans want different things from the series. Metroid: Other M was supposed to unify all those fans, but failed miserably.

For this reason I expect a more Halo-like Metroid title for the Wii U. If the old fans don't like the new Metroid, then the very least thing they can do is make a new fanbase.

I think Metroid is only considered to be one of Nintendo's main franchises because it was one of the first. In classical terms, there was this trinity: Mario, Zelda, Metroid. Of course, Metroid never gained the world-wide recognition the other two did.

Anyway. Over the years, the Metroid franchise is at 17.49m total according to this site, while Pikmin is only at 3.78m. At least Pikmin won't overtake Metroid's lifetime sales this gen. I agree it's likely that Pikmin 3 will sell better than whatever Metroid game comes this generation.

Don't forget, Pikmin in Japan should be big! Hell the remakes of Pimkin 1 and 2 sold 200k each. So I think based on Japan alone, Pikmin Wii U > Metroid in terms of sales

Would need to know more about a potential metroid game before I make a guess (oops, 'prediction')...ie who's gonna develop it.
I'm sure if it was developed by retro, it will be more like to sell than if it's developed by team ninja (just as a hypothetical example)...so it's a difficult one to just call without more info. I do believe pikmin 3 will sell more than previous pikmins though, even if it's not huge. Don't know why.
(slightly off topic I'm still living in hope for a new 2d style metroid game on a handheld at some point)

Pikmin 3 will be the biggest Pikmin in terms of sales. It looks like the most graphically impressive WiiU game to date and it will have a great window of time where it will be the prime focus. But if a completely refreshed Metroid is released, developed by Retro, incorporatign Halo elements like a great looking world, co-op, online multiplayer, outstanding production values... the western market will eat it up and it will destroy Pikmin in sales. Pikmin should be 1-2 million but a high end Metroid could potentially do 5-10. A lousy Metroid... would probably still top Pikmin if is't launched to a larger user base.

Yeah, it's weird.  I actually thought it was a lot bigger than it is, and I know a few other people who do too.  I think it's more a symbolic game of Nintendo than a sells-a-lot-of-copies game.

OT: I have no idea how Pikmin will do, really.  It's gonna be really interesting to see.  I think it can easily outdo the Gamecube versions, simply because it has the advantage of releasing when it is (i.e. during a bit of a drought of Nintendo titles on the console).  

A proper Metroid Prime game has a chance of beating it, but even then, Prime 3 wasn't quite as big as I thought it would be.  Who knows, really.