Emulating N64 games on DS is 100% impossible, but most games could be relatively easily ported to DS. Other games would need a virtually perfect port with every optimization in the book to work, games like Majora’s Mask may be able to handle it if the memory is more efficiently used. That separate video memory on the DS would certainly help wonders.
Years ago Nintendo implemented a clever new way to combine aspects of both Sudoku and crossword puzzles into its unique brainteaser. Picross (short for Picture Crossword) adapted the Japanese creation of nonograms into a treasured series of games. The DS' remarkable was a fresh take on the cute enigmas, adapting the whole thing around three-dimensional objects.
You start each puzzle with a hint of what the final image of the puzzle will be, and then see how many squares within a line should be filled in. Combining logic with trial and error, you eventually create a picture out of whats left; that challenge was deepened immensely in Picross 3D by adding a third dimension to the previously flat puzzles. If you've played all the other predictable puzzle games on the DS, pick up this to get a taste of something different.
Ghost Trick has to be one one of the most original and endearing games on the DS. While it was developed by many of the staff that worked on Capcom’s Ace Attorney series (including series creator, Shu Takumi), Ghost Trick is very much its own game, with a completely different cast, setting, and gameplay unlike anything else on the Nintendo DS. Ghost Trick covers the entire emotional range from heartwarming highs to gloomy lows, and it’s all thanks to solid writing and an excellent cast of characters.