Thinking About the Oath of the Watchers

 So, Paladins are only getting one brand-new subclass in Tasha's Cauldron of Everything - the Oath of Glory is a reprint of Mythic Odysseys of Theros' Greek-hero inspired subclass. The other is the Oath of the Watchers.

We don't have the finalized version of it, but Watchers were featured in Unearthed Arcana. The following is a copy/pasted description of the Oath's flavor:

Paladins who vow the Oath of the Watchers seek to protect the mortal realm from the predations of extraplanar creatures, many of which can lay waste to mortal soldiers. Thus, the Watchers hone their minds, spirits, and bodies to be the ultimate weapons against such threats. Paladins who follow the Watchers’ oath are ever vigilant in spotting the influence of extraplanar forces, often establishing a network of spies and informants to gather information on suspected cults. To a Watcher, keeping a healthy suspicion and awareness about one’s surroundings is as natural as wearing armor in battle. 

Tenets of the Watchers A paladin who assumes the Oath of the Watchers swears to safeguard the mortal realm from otherworldly threats. 

Vigilance. The threats you face are cunning, powerful, and subversive. Be ever alert for their corruption. 

Loyalty. Never accept gifts or favors from fiends or those who truck with them. Stay true to your order, your comrades, and your duty. 

Discipline. You are the shield against the endless terrors that lie beyond the stars. Your blade must be forever sharp and your mind keen to survive what lies beyond.

    So, the basic idea behind this oath is that you're a kind of planar defender - which I'd say also works with most paladin oaths. Ability-wise, the subclass really emphasizes the vigilance and elements based around guarding locations and people.

    A Watcher Paladin can deal with any planar entities coming into their home territory - they can turn elementals, fey, fiends, and aberrations. And they have a number of tools that can punish spellcasters and help keep their allies on their toes and mentally safe.

I'm really fascinated by the idea that paladins of this sort build networks of spies and informants - much more cloak-and-dagger than your typical paladin style.

To me, the fact that aberrations are amongst the things they can abjure really lights up some of my modern-D&D ideas: namely, I think this would be a great subclass for someone terrified of aliens and UFOs.

While the Watcher's tenets bend toward protection of innocents, the real emphasis of it seems to be extra-vigilance and keeping alien (i.e. extraplanar) entities out.

I imagine a person who has a traumatic experience with extraplanar entities, perhaps an abduction or something, and their psyche becomes defined by obsessive behaviors to ensure their safety. Looking Glass from the HBO Watchmen miniseries feels like a good pop culture example. Eventually, they find others that validate their experience and trauma, either of similarly dismissed or ignored victims or some already-extant secret organization that keeps watch.

I think you could play this character as deeply neurotic, but with neuroses built around a fear not just of this happening to them again, but of its happening to anyone else.

I generally like the Paladin class a lot in 5E - the Divine Smite mechanic is very satisfying, and the various protective auras and such are a really nice bonus on top of the martial half-caster frame. And I think I've got my first prospective character should I ever play a modern D&D campaign.