Things older cameras did that new ones dropped, and which of them actually mattered

Nostalgia does a lot of work in these conversations, so here is the split between what genuinely changed the shooting and what people just miss.

Genuinely worth missing

• Dedicated dials you can set with the camera off. Shutter speed, aperture ring, exposure compensation, all readable without powering up or looking at a screen. Modern bodies bury these in menus that need the camera awake.
• A hard switch rather than a menu item for the things you change constantly. A physical drive mode dial cannot be changed accidentally in a bag and can be set by feel.
• Optical viewfinders in bright sun. Electronic finders have improved enormously and are still worse in direct light.
• Battery life measured in thousands of frames, because there was almost nothing drawing power.
• A body that works fully without a menu system, which meant borrowing someone's camera and using it immediately.

Not actually worth missing

• Fewer autofocus points. It was not a feature.
• The look, which is lenses and processing rather than the body.
• Slower operation as a discipline. Some people genuinely shoot better slowly, and you can shoot slowly on any camera.

What is worth checking on a new body
Whether you can change the three settings you actually use without entering a menu, and whether the controls are usable with gloves. Both are testable in a shop in two minutes and both decide how much you enjoy using it for years.

The unglamorous ones nobody lists: two card slots, a battery that is not proprietary to one generation, and weather sealing that is specified rather than implied.