1. How it handles the two screens
The DS has two screens, and that’s where emulators differ most. A good one lets you choose their layout (stacked in portrait, side by side in landscape) and adjust their size. Without that, you’re stuck with two small fixed screens that are hard to read.
2. The touch screen
The DS’s bottom screen is a touch screen, and many games depend on it. The emulator has to send your taps to the right screen, accurately. Check that the touch area is correctly mapped to the bottom screen.
3. How safe your saves are
Losing a save is one of the most common complaints among emulator users. Look at three things: are your saves stored locally, written reliably, and can you import an existing save (.srm) from another emulator? iCloud sync is a plus for getting them on your other devices.
4. Controllers
For long sessions, a Bluetooth controller (Xbox, PlayStation, MFi) changes everything. Check that it’s supported, and that the on-screen controls hide automatically when one is connected.
5. App Store or sideload
Some DS emulators are only available via a sideload (a third-party store like AltStore). Others are native on the App Store: you download directly, no extra step. Up to you, but native is the simplest.
What about Retro Pal?
For context: Retro Pal ticks these five boxes. Configurable dual screen (portrait or landscape, adjustable size), bottom touch screen, local saves with .srm import and optional iCloud sync, Bluetooth controllers with automatic hiding of the on-screen controls, and a direct App Store install. DS emulation is powered by melonDS, at 60 frames per second. It’s our app, so take that for what it is: weigh it against the criteria above.