There are two difficulty modes - 3DS and N64. The 3DS mode is supposed to be tweaked to be useable with the optional gyro controls while the N64 one replicates the original game, but we couldn't tell the difference. The levels are only unlocked in high score mode for whatever setting you found them on in story mode, which is a significant incentive not to go switching between them. We stuck with the N64 one for the most part.
In a spin
The gyro controls aren't great. It all depends how much you can stand waving the 3DS around, but as the entire game involves movement we found them much less useful than the motion controls in Ocarina Of Time. You'd probably have to turn off the 3D if you were to use the gyro controls for any length of time.
The quality of the visual upgrade Star Fox has received on 3DS is variable. The water effects are fantastic, particularly on the aquatic world of Zoness. Explosions look great and the 3D effect is always solid, but in several places the game's N64 roots are all too obvious.
The space sections, which we had hoped would be spruced up with a better draw distance to enable us to really get a sense of the depth of the level, are absolutely riddled with pop-up. This is probably to preserve the gameplay rather than because of any technical issue, but it still looks incredibly rough. Rougher than on N64, even, thanks to the sharpness of the 3DS screen that accentuates every object as it pops into view in the middle distance. It's noticeably old fashioned in a way that Ocarina certainly is not.
But great gameplay shines through, and Star Fox 64 3D has some superb moments. The high score mode aside, there's little more the developers could have done with it, and after getting to know it all over again we can see why Nintendo took a step back after this. It was an impossible act to follow.
Moments of brilliance, moments of frustration, and masses of replay value. They don't make them like this any more - they remake them.