Some of the Diablo 3 characters will be better in close combat smashing people with swords, and axes, others from afar with arrows, or magical spells. But each character will be unique and a different experience when you play with it.
Now lets learn a little bit about each Diablo 3 character...
First off lets start with a returning favorite, from Diablo 2, "The Barbarian"
The barbarian in Diablo 3 is a character of brute strength, and amazing skill. He has warcries, and powerful melee skills, with few distance attacks. The best way to fight with the barbarian is to power yourself and anyone other characters in your party up with warcries, then as fast as you can close the distance between you and your enemies, with the barbarian once you have closed the distance there is no stopping his power.
The best counter for the Barbarian class is a Wizard, That can teleport away, and freeze the Barbarian.
This brings us to our next D3 Character...
The Wizard is a powerful being, with intelligence beyond any other character in Diablo 3, best known for its destructive and powerful magic, the Wizard is great for crowd control, but must be kept as far away as possible from its enemies, once the enemy of the wizard has closed the distance you will notice how fast the Wizard Class dies.
The Wizard has 3 main spell classes, FIRE, Ice, and finally lightening, each with unique and devastating power.
The weakness of the wizard would be another strong class from a distance, or someone who can get to the Wizard fast.
The monk is a powerful class, with capability's of healing, and dealing great damage. The monk can heal himself his allies, or do great damage to any foe. He is a holy man, with great powers against undead creatures. The monk is much like the paladin from Diablo 2. From my understanding the monk will be able to cast great auras, like the paladin, the auras will be able to inflict damage to foes, or help buff up the group.
The weakness of the monk, is anything that can inflict damage faster then he can heal himself.
The Witch Doctor:
The witch doctor is an odd character, similar to the necromancer, as he used undead monsters, and evil powers to do his bidding. He can arise great armies from the monsters he has killed, as-well as cast powerful spells to devastate his foes.
The Witch doctor much like the Wizard is weak if you can get to him, but first you must break through his armies, and his spells.