The best raid buffer, delivering 3% crit on a single target, a blessing and they can keep up judgement of light and judgement of wisdom cast by two other paladins on a target. They are somewhat less powerful compared to some other classes in 10 mans, but who cares about 10 mans in tbc?
The DPS is sub-par, and while allot of people comment that wind fury is required to deal decent damage. The windfury spot is better given to a different melee dps, particularly so if you have a protection paladin in your raid so you can lend away some bonus holy damage. Even so, few guilds have 25 people with 100% attendance, so the few times you're put in the melee group with all the related group buffs such as battle shout and wind fury, you should be able to get into top 10 if your gear is on par with that of your guild. Play style is a bit bland, and the way you pick and choose your gear upgrades have few if any intricacies, just pick up the slowest weapon you can find and auto attack. There is the topic of seal twisting, which is a relatively advanced concept for the time and the mechanic is a bit convoluted. I suggest you hit up the thread regarding seal twisting.
For pvp, you perform quite well in battlegrounds. Retribution paladins can cause problems for practically all classes, with cleanse, bubbles, blessing of freedom, a stun and an incapacitate effect. You're well suited when your enemy don't communicate via voice. In arenas however, while Retribution paladins are playable. The skill requirement of you, and your partner(s) is unreasonably high compared to most other speccs in the game in order to reach the really high ranks. You will not struggle too much if you're a skilled player hitting the rating requirement for arena weapons, but you will seriously struggle acquiring the most recent arena shoulder piece.
For someone that enjoys Battlegrounds, playing as Retri paladin in pvp back in the day was fun. But the gear acquisition was nothing but a chore.
Edit: Rightfully so, guilds will not allow more than 1 retribution paladin in the raid at any one time. I don't know how popular Ret is atm, but i would not bother trying to join a guild with a raiding Retribution paladin.