3DS can still blow the PSP out of the water when it comes to graphics. I especially can't see the reasoning behind PSP being on par considering PSP can't even do ports on par with some of the mid-tier PS2 games. Snake Eater 3D at the very least seems like a solid port of the PS2 game so far (one of the best looking games on the PS2). But there are better looking games. It seems many people forget about Super Street Fighter IV 3D and Resident Evil Mercenaries 3D. Later on RE Revelations. I could name numerous more as well. You can't blame the 3DS for lack of effort on certain developers. It can certainly pull off exactly what we were seeing in tech demos, we have actual finished games (or upcoming games that are not tech demos) to show us this much.
From what i can see, MGS3D is mostly on par with PS2 graphically. Some things are slightly worse than the PS2 version (namely textures and some very minor polygon downgrades), but there's some clear shader effects that are superior to PS2. Definitely balances it out imo. It's also not finished yet, and many effects are often added in during late development. Not fair to judge it quite yet until we've all seen the final product. On the actual system as well (which will inevitably look better than a video or screen can show).
To be quite fair, while the Naked Snake tech demo certainly pulled off great character models, some of the environment detail left much to be desired. For example-
Snake looks great, and some environments look good too. But others in the demo looked just bleh. Looking past the characters, you've got some weird looking environments. In this respect, i'd have to say that the newer version looks better.
The biggest issue i have is that Konami and Kojima were quoted as saying that if they had more time, they could make the actual game look even better than the 2010 tech demo. My guess on the matter is that perhaps this game was outsourced to less competent developers and they decided that instead of remaking the game as originally invisioned, they decided instead to just port the PS2 version. It's possible that Kojima and the team that led the tech demo have nothing to do with this new version.
At any rate, don't diss the 3DS' graphical power just because one developer (or however many) lack the effort to push the system. Personally, when i ignore the 2010 tech demo, i'm still somewhat impressed that the 3DS can actually come on par with the best that the PS2 could do. Especially so early in the 3DS' life. I'd say Snake Eater was second only to Shadow of the Colossus graphically. And i'd only give SOTC the win due to how far the developers managed to push the PS2's hardware, i still feel MGS3 has the overall superior look. It should also be remembered that the 3DS has to process the 3D effect, meaning it has to render the graphics twice (or around that). And that this is still VERY early in the system's life.
And no i'm not bashing the PSP. I actually love the PSP and it's definitely the superior gaming system so far (until the 3DS gets a better library at least). This is purely an analysis of the graphical power, which doesn't actually matter when comparing gameplay. Take note at that.