The Touchscreen of the 3DS has degenerated to a backlighted touchpad in most games.
In most DS games, the lower screen was the main screen with direct input. If there was a target/object/NPC shown on that touchsensitive main screen, you could directly tip on it to get a result. Investigating rooms in Ace Attorney 1 - 4 or Hotel Dusk, defending the train/boat with a cannon in Phantom Hourglass / Spirit Tracks, and so forth.
The mainscreen of every 3DS-game is the upper widescreen. You can no longer tip directly on interesting/suspicious objects in Ace Attorney 5 to get more information (or a funny response)... instead you have indirect control over a cursor on the upper main screen, which follows your gestures on the lower screen. Much less intuitive than the DS solution or touchscreen games on other mobile devices.
Both 3DS screens should have been (multi-)touchscreens!
