I know the majority of the forum isn't into the From Software games, but I got the Old Hunters DLC last month and it is FANTASTIC.
I'm not going to spoil specifics about anything, but I'm going to give a breakdown about how much is new:
-around 10 new trick weapons (I forgot to count) which scale with a variety of builds. I'm particularly fond of the Bloodtinge weapon
-a variety of interesting sidearms, including a Gatling gun and a new shield
-new spells, one of which scales with bloodtinge instead of arcane.
-3 new areas of increasingly creepy design.
-5 new bosses who are so hard I only beat one of them solo so far. One reuses an old boss model, but the model is among my favorites and the new features of it are awesome.
-3 new Oath Runes, one for enhanced NPC summons and 2 that enhance the movesets of two specific weapons and change your hunter's appearance.
-Frightening new enemies and intriguing new NPCs.