Some modern ports like the semi-recent SNK arcade collection rework them into twin stick shooters, aiming with the right analog stick for rotary-precision, which actually makes them easier than the originals, if not authentic. If you load such a game up in MAME there's no decent way to map the controls on any normie controller. The old, contemporary ports just screw up the controls entirely, Genesis version of Midnight Resistance being a particularly big offender. I don't even have it in my to explain the control schemes in that game, but trust me they're all WOAT no matter which option you pick.