LogFAQs > #932091271

Just for a little background on the development of 1-5 -

The first three AA games were for the GBA in 2001, 2002, and 2004, all Japanese releases only. In 2005, they made a DS port of the first AA game, and then added this case as a bonus to the end of it, which made use of fancier visual effects and gameplay mechanics (you'll see) that the DS offered, and this game is the one that we got released worldwide. It was one of the first DS titles, so it was back at in that time when "you can do stuff on the DS's touchscreen!" was the big selling point they were trying to push in every single game they released, so they made it sound like Phoenix Wright would be a game about doing detective mystery stuff on the touchscreen, when in fact there's about five minutes of it in 1-5 and that's it. Come for touchscreen shenanigans, stay for the surprisingly engaging story

Anyway, since 1-5 was created later than the other cases in the first three games, that kind of explains why it has a different feel. It jumps ahead a bit in the development of the series' maturity.