Side by side comparison between Metal Gear Solid: Snake Eater 3D, released for Nintendo 3DS in 2012 and Metal Gear Solid 3: Snake Eater - HD Edition, released for PS3, Vita and X360 in 2011. Snake Eater 3D was emulated in High definition.
Totally, I was going to say its unfair to upres the 3DS version for comparison but it doesn't actually matter because it looks stellar anyway, I think the only glaring thing is the resolution of the some of the alpha textures (for leaves on trees), but its not a big deal at all.
Amazing considering the 3DS top screen is 400x240 (per eye), so the assets of this game were meant to be seen at 240p on a very small screen but if you blow up the res to 720p (Guessing since PS3 version is 720p + 2xMSAA) it still looks great. I'm genuinely surprised at so many of the effects staying intact when I feel like you might not even be able to perceive many of them on a 3DS screen.
It's beautiful in 3D. My only real gripe with it is the performance, especially in when fighting The Boss at the end. Even running at n3DS clocks the framerate is so bad that I had to resort to hiding in the flowers and taking potshots, engaging her in CQC was basically impossible.