Having driven Town Cars extensively, I can say they are straight forward and relatively easy to fix and reasonably reliable. If you run a limo business they are probably your best bet, as long as you maintain them.
At the same time they are by far the most behind the times of any cars sold in the US in terms of modern technology. Unit bodies with modern crash design and independent rear suspensions in cars (not trucks) are here to stay. If you look at current road tests you will see these cars (including Grand Marquis and Crown Vic) are pretty much the poorest in their class.