The Halberd is a two-handed poll type weapon ranging in length for 4 to 6 feet. They are essentially an axe with a spear continuing out the top. Used for both cuts (with the axe part) and thrusts (with the spear) they made a quiet adaptive and very deadly weapon. Being a poll weapon their range of attack is further out. The extension on the back of the axe made an excellent hook for bringing down opponents on horseback as well as catching up other foot soldiers. A Halberd in the hands of a well-trained master is a deadly thing. Every bit as deadly as a sword or rapier.
Personally I have never tried fighting with a Halberd, but they certainly are fascinating weapons. I would use this type of weapon for medium weight characters or even lighter weight ones with the smaller Halberds.
In Barbara Hambly's book "Dragonsbane" (a book I highly recommend), one of her main characters, Jenny Waynest, wields a Halberd.