A druid is like a warrior.
You have zero rage initially.
But as you take damage, your rage builds.

A paladin starts with full mana.
But using abilities depletes it.
You replenish mana, as you tank or are healed.

The druid seems to have a larger health pool.
Not sure if this will be true in Cataclysm.
You're still crit immune from talents alone.
Agility and Stamina are important.
And dodge is your main mitigation factor, as you cannot parry or block.

The paladin works on Holy Power now.
Which is similar to rogue/cat energy.
Strength and Stamina are important.
Talents get you crit immunity now.
And you can dodge, parry and block.