LogFAQs > #967934703

I will say I recommend at least checking out Priscilla and Gwyndolin's fights on YT if you don't intend to fight them. They have some pretty unique boss fights that definitely stand out at least to me.

Gwyndolin Lore - So he's actually not the god of war. Gwyndolin is actually Gwyn's youngest child and was basically left behind to protect Anor Londo. He wants to maintain the glory of his father's kingdom, so he casts an illusion on the city. This is all to convince the Undead that there's still hope, regardless of how dire the entire world is. This is also why he chooses to speak through Gwynerve as opposed to himself as she's more of the uh 'approachable type' and is likely to convince the Chosen Undead to continue their quest.

Killing him reveals the true state of Anor Londo and it's a cool implementation of a secret boss. There's also a pretty big fan theory that Ornstein is also an illusion, There's quite a bit of evidence against it, but I personally like the idea that Gwyndolin is doing everything in his power to keep up this illusion that everything's okay.

As Cassandra stated, you do get a unique Covenant for killing the Four Kings before getting the Lordvessel. (You have to kill the guy in New Londo to get the water drainage key). You also meet Kaathe, who basically hints at an alternate ending. You don't need to do this for the second ending though.

As for the lord souls I usually go
Seath > Bed of Chaos > Nito > Four Kings

I just always get lost I'm New Londo Ruins so I'd rather do it when I'm overleveled.