Fond memories of the series aside, a new game needs to have manually-designed dungeons and more fleshed-out sidequests that don't feel like annexes to city-building. The music itself could use development, though keeping the spare instrumentation of the first game + proto-Layton stylings from the sequel would be ideal. Art-style should stick close to 2 but with 1's variety in locales (the Egypt-like village and dungeon was great).