According to Vetron's Guide to Weapons and Armour, the morning star has a "5" effectiveness rating.
Morning stars have been a part of the series since Ultima V and remained unchanged through the tests of time. In their first appearance, they were actually capable of striking enemies through walls.
A "mace on a chain" is the morning star, which reaches over obstacles to smite thy foe at range. One blow straight on from this and the enemy is out till morning -- at least.
A polearm is generally a stout wooden or metal staff topped by a metal cutting or bludgeoning fixture. The morningstar, a variation on this theme, consists of a staff with a chain attached to one end, and attached to the chain, a heavy, spiked bludgeon. Morningstars, halberds, and other polearms are prized for the damage they are capable of doing and for their long reach.