Druid is an interesting prime class to play. At low levels your shift forms are pretty poor fighters and you will find yourself largely a support char, depending on the rest of your class order. Druid prime shifting is superior to non prime shifting and the shield of thorns spell at high levels helps with shifted combat greatly. Druids are able to solo very large mobs by harnessing the power of the vast mana regen. They shift into a combat form and fight until their hit points get low. Then they exit from combat, return to human form to heal themselves up and then shift again. It's a nice class in that you are able to operate solo through the power of your shifted forms, but you are welcomed into groups because of your good mana regen.
Supplementing druid class:
Cleric isn't absolutely necessary for druid prime, but it still helps greatly. The cleric spell aegis and supplication pets are very helpful.
Mage is a popular addition to druid as you will want to be able to harness your high mana into blasting in a group.
Warrior is not hugely popular for druid primes, because they depend largely on their shift forms when soloing, and act as supplemental casters in groups. However warrior is still a good addition if you're interested in balancing out your character to be able to fight melee unshifted for running smaller mobs and coins, etc.
Monk is nice for balancing out a caster prime because it adds toughness and gives an initial attack.
Thief is also not widely chosen by druid primes, but again it helps to balance out the melee capabilities of the character.
Necromancer is a popular choice because of helpful spells like wraithform and spectral shield. In my opinion druid prime isn't really cut out for using large necropets. If you you're taking necro to fight with pets, perhaps add warrior or monk to the class order as well. Necros are drawn into combat by their pets.
Bard is a very nice supplement to druid. Bard songs are very useful to a group. Bard is a non caster class and has more hp, better armor, and can protect. Also very important is that Bard can glance into mob inventories.