In vanilla, paladins were primarily looked upon as healers with Holy being the tree that promised them being useful. When original Naxx was released, in 1.11, that changed slightly, with pally tanks being fairly optimal for some of the AoE pulls there, but I don't recall them still being considered much for main tanking any of the bosses, in Naxx or anywhere before. And Ret... well, without some really incredible gear, Ret was just lawlcakes on the roflcopter.
IIRC back then, Righteous Defense was the only "taunt" Paladins had. Seals were, I think, 2 minute duration, and expended with the use of Judgement. There was only one Judgement, and it would place the effect of the current seal; there was no Seal of Vengeance/Corruption paired with Judgement of Wisdom or Light. I know talents have been INSANELY overhauled; BoKings for a long time was only accessible to Prot pallys. Rather than Hand of Salvation, there was a Blessing of Salvation, which was a 5? minute buff for a constant -20%? aggro.
And so, so, SO much more. I never actually played a pally in Vanilla (at least, not beyond lvl 12) and only ever now and then in BC, so most of what I know of oldschool paladins just comes from raiding with them.
But yes... there have been a lot of drastic changes over the years. IMO for the better. I love my Tankadin. :3