Does Bloodborne Old Hunters change the main game in any way?

I'm starting my Bloodborne NG+ tonight after purchasing the DLC. Without going in to major spoilers, are all the new items and weapons only placed in the DLC area? Or have the added stuff to the main game as well? I'm wondering if I need to look through every corner of the old areas for new secrets or just mainline it to the new content.

Content wise, the DLC adds a lot of new weapons and some really powerful gems.

If anything, the DLC actually adds a lot of lore that sheds some light on some unanswered questions.

I was curious about this as well. I stopped playing Bloodborne around 3/4+ into my first playthrough, so would it be a good idea for me to jump into this DLC before I finish the main game? Just curious...

Someone might have to correct me here, but I think finishing the main story immediately deposits you into New Game + with harder enemies (and greater rewards). It might be ideal to do the DLC before you get much further.

All the new content is limited to the DLC area.

I thought I heard that the new mechanic of summoning NPCs was applied to some or all of the boss fights in original Bloodborne but it's possible I'm mistaken. I'm pretty sure The League is accessible to people without The Old Hunters, so I'd be surprised if the summoning NPCs part of it was only for DLC content.

Finishing the game does indeed dump you into NG+ where enemies hit much harder and have a lot more HP. The difference is most noticeable when going from your first to second playthrough, and then each subsequent playthrough is a lot milder. These aren't exact numbers or anything but I'd say enemies get about 60% harder (more HP, hit for way more) going from 1st --> 2nd playthrough and then it's like a 5% bump each subsequent completion.

So If you're decent level - I think Brad said the recommended level is 70 for the DLC - then you should probably jump into it before going to NG+

Yes this is true. New NPC summons were added into the base game areas.

EDIT: Also yes The League stuff is available without the DLC. I did The League stuff before the DLC came out.

If nothing else this makes me think I should go back and play some more Bloodborne. I've only put around 15 hours in so far and never even felt like I saw half the game! Maybe I should throw some money down on this and continue with the main game?

Do the new weapons come into the main game at all? Will I get better drops if I've purchased the DLC and, if so, should I wait to purchase?

There is gear that can only be picked up in DLC areas.

@golguin: Excellent! Just worried how some DLC makes the main experience trivial (Though that's doubtful with my memory of trying to play Bloodborne!)