I’ve seen a fair amount of complaints about how the 3DS will suck for first person shooters, because it doesn’t have two analog sticks.
Various suggestions in reply to those complaints have been made, along the lines of “it has accelerometers” and “it has a touchscreen.” Honestly, I think both of those solutions aren’t satisfactory, because the accelerometers might put you out of the 3D sweet spot, and the touchscreen gets your hands away from the controls.
However, there are plenty of controls available that don’t have that problem.
Use the slide pad for aiming, of course. But, rather than use the touchscreen or the accelerometers for movement (or vice-versa,) use the A/B/X/Y buttons for movement. In PC FPSes, using digital buttons is acceptable for movement, so why not on the 3DS?
Now, you’ve got two hands solidly on the console, one for aiming, one for moving. Oh, and you’ve got the L and R triggers under your fingers, so now you can get primary and alternate fire.
As for switching weapons, well, you’ve got the D-pad that’s not in use, for left-handed weapon switching, and this is also a good use of the touchscreen – have all of the weapons displayed on the touchscreen, as well as data that would normally be in a HUD, keeping it off of the main display.
This way, you’re effectively using every control except for the accelerometers on the console, you’ve got a solid grip on the console, you’re playing with the most convenient controls for an FPS that are on the console, and secondary controls are effectively used for secondary functions.