Speaking from the perspective of driving Lincoln's on a daily basis hard use for about 5 years as a limo driver. Also as an owner of several.
We had one on the fleet that had 500k miles on it. They are very comfortable and for the most part reliable cars.
The bad:
Headliners - they seem to become delaminated and droop after several years is my experience on several
Paint on some - fades and flakes on hood and top and trunk, (may be certain years)
Rear suspension - it's a fucking nightmare. They are ballast bags that wear out over time and leak causing your ass end to drag and look unsightly and need replaced, high dollar. We learned a trick to just replace them with Crown Vic springs to fix the problem permanently. The ride wasn't noticeably impacted.
A hard use car has the door opened and closed more than normal. The weight of the doors (heavy) wear and shear the pins that hold them on. Seen it on more than one but not as much as the other issues I'm pointing out.
Head light switch - wears out, starts becoming temperamental. Seen it on many, a bitch to replace.
Ignition actuator wears out - try to start vehicle and nothing. Hard problem to diagnose unless you're familiar with it. Take it to dealership they had difficulty troubleshooting it. Charged me for parts and labor it didnt need. Seen this on several vehicles.
Heater system - there's a flap that directs the air, it has an actuator that wears out under the dash. You have to take the whole fucking dash apart to fix it, fuck what a pain in the ass. Seen it a few times.
And the # 1 fuck you that drove me to Honda's was a plastic intake manifold that cracked, Fuck you, fuck you, fuck you... Total my town car over a plastic manifold, fuck you... Rotten cocksuckers, fuck you.
Ok so they went to the new body styles in 1998 I think... All of my experiences were with the older body styles. They may have fixed some of the issues and not others, I don't know.
I would consider owning another though. All in all I loved the ride, and for the most part they were dependable. I was able to get well over 200k miles on them before I started thinking about replacing them.