No class changed more for leveling than the 
Paladin. Here's what Blizzard's Paladin class post changed and what it means.
New buttons early
- Holy Strike at level 6: an instant melee strike that deals Holy damage.
- Seal of Fury at level 10: a tanking seal with an absorb shield and a 10-yard Judgement taunt.
- Consecration at 20, baseline for everyone.
Seals and Judgements
Judgement no longer uses up your Seal, so you stop recasting it all the time. Seal twisting is no longer a baseline trick. Blizzard removed Twist of Light in its 3 November notes, and the Retribution capstone is now Unsealed Wrath, which stores your Seal for later swings.
Support
Blessing of Kings is baseline. Blessing of Salvation and Blessing of Light are gone, and tank threat was raised to make up for it. Lay on Hands is down to a 20-minute cooldown, and resistance auras reach raid members within 30 yards.
Who should play one
If you want a tough leveler who can tank or heal in dungeons, a Paladin is now one of the best choices. Horde players can be one for the first time as 
Undead. See the Paladin leveling guide for how to get to 60.