Any of the 2d ones? 

Nope, but i did get through the entire story campaign of resident evil 4 when i was 12 years old without guides, so that warrants my status as a hardcore gamer ;-D

Then I  recommend at least trying super metroid, fusion, or zero mission on an emulator. Who knows if you liked other m you might love these. Fusion would be the easiest to get into. Metroid sidescrollers are about as different from the prime series as Zelda topdown is from 3d camera Zelda's or 2d Mario from 3d mario.

What if they make Metroid both a 3DS and Wii U game with differences in graphics and slight gameplay/mode changes, like Smash 4? They might be under the impression that it would offset the cost of making an expensive HD experience, which is pretty much true.

I hope not. I'd prefer Metroid to be tailored to a specific console with a specific style. Metroid is a series that would probably benefit from an "expensive HD experience." Its most appealing feature is its atmosphere. 

Well, it would still be an expensive HD experience on the Wii U, it's just that the 3DS version's sales would bring in most of the profit.

Regardless, I agree that I would rather the games be tailored to their consoles (like, 2D side scroller for 3DS and first-person HD for Wii U). This is also a big possibility. 

MP2 is harder though. Probably the hardest Metroid game. Not very newbie friendly.

Idk I've seen Titanfall, Forza Horizon 2, Last of Us Remastered, Little Big Planet 3, Halo Master Chief Collection being labeled as exclusives despite all of those games being on the previous gen console as well so if they get a pass than I don't see why we can't call Smash Bros 3DS an exclusive.

SSB for 3DS is exclusive. Different stages, modes, music and trophies

I predict Other M ported to New3DS, with using the stylus on touch screen to activate first person mode.

It would be one of the best troll for Nintendo ever, but to be honest I would'nt mind it that much (except for the fact that it would probably mean still no new metroid for a while)