None of them. To be blatantly honest, none of the other games need remaking.
In the graphics department, OoT is the only bad looking one. I mean, those graphics are horrible, BUT since it was the beginning of the 3-D era, it is excusable. The 2D one's look really nice because they are 2-D and they knew the technology better, and the 3-D one's all look nice except the aforementioned game. So when it comes to that, they really don't need remaking. Now you could argue that you want a 3-D version of the 2-D games, but that would just be awful. The 2-D and 3-D games play VERY differently from each other, and as such, aren't really interchangeable. There's more Darknuts in one room in the original Legend of Zelda than the entire first dungeon in Ocarina of Time. The 2-D games were very combat centric, and as they did have puzzles, they weren't as challenging to figure out the solution to.
I guess that paragraph also sort of covers the gameplay.... the only other thing I can think to mention would be the fact that there's nothing wrong with the gameplay as is, and it really needs no polishing or fine tuning. I mean, maybe they could make aiming in Majora's Mask with the bubble and Bow a little better (which, by the way, could have easily been fixed by adding crosshairs), there's really nothing wrong with gameplay, not by a long shot.