The biggest improvement was getting away from carburetors in favor of computerized electronic fuel injection. Until that time cars were horribly unreliable. Stuck automatic chokes, flooding, poor fuel economy, all were the nasty by products of carbureted engines. Back then it seemed every car had it's own "method" of being started. Some you had to pump the hell out of. Others you would flood if you did the same, especially when warm. Vapor locking in hot weather was a common occurrence. In general they were nothing but an undependable pain in the ass.
Now you simply turn the key, or on the newer models touch a button. As soon as the first piston comes around to it's compression stroke, the cylinder has a proper charge of fuel and air and the engine fires, and runs at the proper RPM without even touching the throttle. In 20 years I've never had either car turn over and not start immediately. I can remember walking to school in the 60's after the first cold snap. At most every stoplight cars sat belching black smoke, chugging away from stuck automatic chokes. Spark plugs were lucky to last 10,000 miles. Now they last 150,000. Fuel injection and unleaded gas are the biggest reasons as to why.