Here are my thoughts from the final game (I got it last week):
-Differences from the demo? Little-to-no difference. Same frame rate hiccups. General gameplay seemed pretty solid, but the demo and final build chugged in the same spots to the same degree. Disappointing, especially since the game DOES look better in quite a few spots in 3D (nice shaders used to make stuff pop more).
-Runs and looks much better than Peace Walker; slightly better than PS2 version in some spots, worse in others due to the lower resolution.
-Performance-wise, the 3DS version doesn't have the motion blur effect to mask the lower framerate in cut scenes, which the PS2 version used heavily. So, it looks choppier.
-ALL dialogue is voiced and present.
-Only two control schemes, one with CPP and one without it.
-This game is also wayyyyy better than Revelations at detecting the CPP and making sure it reactivates when you come out of sleep mode or load a game. Unlike Revelations, you don't have to enable it in the options every time you load your game. The game checks if it's there every time.
-I'm very susceptible to 3D, and the effect is impressive here.
-You can store 12 photo camos. The game accesses your 3DS photo gallery and uses the pictures from there.
-It is possible to get 100% camo index with a photo camo.
-Yoshi replaces Kerotan; and they moved them to different locations.
-Game tracks all your stats in real time, which is a huge difference from the original. I remember thinking I had 0 alerts back in the game, only to complete the game and find out the game recorded 1 at some point.
-Game also tracks your stats across all play troughs.
-Extreme difficulty = game ends when spotted.