It's just a mechanically solid class that can take on a lot of challenges, with stats that line up well with the Social aspect of the game and the fact that you don't need to spend your Smites until you know the result of your roll so you can wait until you get a crit.
Most effective class that's not a full caster? (Doesnt need to cast at all, can just smite & lay on hands.) Hits the classic knight-in-shining-armor Authurian archetype pretty squarely? Can make a saving throw now & then?
It's the long rest warrior class basically (in 5e).
It can nova. And some of the smite options and spells give some extra useful choices.
The fighter gets to shine in the encounters where everyone else is hoarding their long rest resources (ie. the ones that don't really matter). The paladin is the warrior class that gets to shine when it really matters.