Mario 3D - if SMG didn't exist, I would have to say 2D

Zelda - tough decision. I like them both equally. Zelda Phantom Hourglass is the way to go. Perfect balance between 2D and 3D.

Metroid - if you're a platform fan 2D, if you like fps then 3D

Mario is best on the 2D to be honest. I love Mario 64 and Galaxy, but it feels like there is a strain on the game. There were a number of levels in Galaxy that, while 3d in appearance, ended up playing as if they were 2d. These levels also felt the most natural.

Zelda = 3d all the way. Zelda has always been an exploration adventure game to me. In the 2d versions the best games were the overhead ones that allowed the most exploration: Original Zelda, Link to the Past, Link's Awakening. By the time you got to SNES and gameboy, you already had essentially incorporated a semi 3d feel to the game. Ocarina of Time and Majora's Mask simply gave the graphics to support how the game was already being played.

Metroi Prime = Probably 3d. I haven't gotten a chance to play Metroid Prime 3, and i have otherwise avoided FPS, so I'll save my judgment for it on that.

One thing to keep in mind is 2D's main advantage over 3D is that it is much much easier to tell distance. This is main problem with 3-D platformers.

Mario - 3-D: 2D Mario's gameplay is defined by power-ups and momentum based jumping (and of course brilliant level design and pacing). Galaxy showed that power-ups could work just as well in 3D. Momentum is fun thing to master, but it really doesn't bring that much more to the game. On a whole, Mario games are also retreating from being about making clutch series of jumps so the main advantage of 2D really isn't that strong. On the otherhand 3-D allows for greatly superior exploration (M64), and can make for just as riveting linear sequences (SMG).

Zelda-3D: I'd say the core of zelda is puzzles and using items. Both of these elements really benefit from being 3DD. Overhead view in contrast to 2D really has no significant advantages over 3D.

Metroid-2D: Metroid was about power-up based exploration. Although the Prime series is quite excellent, its never quite captured this gameplay with the same subtlety as its 2D counterparts. In contrast to Super Metroid (essentially the pinanacle though Zero Mission does a great job of reusing its elements) Prime's use of the power-ups is extremely heavy-handed; most all of its physical navigation is extremely limited in comparison to 2D Metroid. Even the one power-up it implements superiorly to 2D metroid (The spiderball from Metroid 2 for the GBA) confines you to very obvious, predetermined tracks. I think Metroid may one day be best in 3D, but until it can properly implement the vast array of Super Metroid's power-ups I'll always think of 2D as providing the superior Metroid experience (I'm waiting for my speed booster, shinespark, and single-wall wall jumping in Prime =D)

 Yep.

2d/3d for Mario and Metroid

3d for Zelda, though I have yet to play ALttP, so my mind may yet be changed.

Mario: 3D. I like 3D mario games, but I have only played SMB and SMB 2 so I don't know how Snes and SMB 3 are.

Zelda: Tie. I loved A link to the past, and PHantom hourglass is marvellous. I would say the 3D games are slightly better, but not very much.

Metroid: only played 3D

I can go back to Mario 2D (loved NSMB). I also love the 3D games.

Zelda in 2D, I don't think I could do it. While I have played every console Zelda, I just loooove that transition to 3D.

Metroid never should have gone to 3D. I stand hard and fast that the Metroid franchise has died because of its first-person aspect. GIVE ME 2D!

mario = both

zelda = both (slightly leaning towards 3d tho)

metroid = 2d

 = Win

No way in hell I could go back to a 2D Zelda, 3D is the way to go :P (gimme more adult link though damnit >< )

I think Metroid got butchered SEVERELY, I have to dissagree with the above poster and say they didn't perfectly mold that one at all >< I LOVED SUPER METROID!!! The platforming was great, the techniques were friggin awesome!!! I miss skrew attack damnit >< Metroid used to be a great blend of Action and Platforming, then they turned it into a generic FPS with "adventure elements", I hate exploring in first person!!!

And as for mario is concerned I could go either way :P  

Mario works in 2D and 3D. He's cool like that.

Zelda- I can play a 2D Zelda game on a portable, but there's really no doubt in my mind that this series belongs in 3D.

Metroid is a strange beast. I love it in 2D. I love it in 3D. I think it should be a third person 3D adventure, despite the success each game has been. I'm gonna have to say 2D, for now.