QUOTE(Destri Melarg @ Feb 6 2013, 06:19 PM)

Dawnguard makes changes to the regular game?! Oh no!! I guess I'll have to make a guinea pig character on someone else's PS3 before I commit to it on my own.
It does make changes to the vanilla game. The biggest ones are to the vampires. All of the existing vampires get a face lift, in the form of glowing eyes and sunken cheeks. There are certain npcs out there who are vampires, but are masquerading as normal (I am not going to use names, so I do not spoil anything for anyone). Before they looked just like anyone else, and it was really hard to tell. Now it is very blatantly obvious they are vamps.
Another are that vampire dungeons get things added. There are new critters that get put in them, and the vamps themselves all get new outfits to wear (some rather nifty vampire armor). So if you have mods that edit the vanilla vamp lairs, they might conflict with DG.
Then you get some new places added. The biggest impact IMHO is Castle Volkihar. It sits out in the Sea of Ghosts north-west of Solitude, right across from the fort with the Thalmor in it (not the embassy, but the place where they torture the Greymane son). You cannot look out at the sea without seeing it rising up. It is an eyesore if you are on the PC and use the high res texture pack, as the two conflict, resulting in the game using a low res LOD for the castle which really looks ugly. Thankfully that can be fixed with mods though. If you are on a console, I suppose it just looks like everything else (yes, I am spoiled by PC graphics).
DG also adds a boatman to several of the port cities (Solitude, Windhelm, and Dawnstar I think?), who you can hire to transport you to any of the other cities.
Hearthfire also makes some changes as well. Most notably to the three places where you can build your house. Any mod using those spots is going to conflict. It also changes the carriage system. You can now hire a carriage to take you to any of the hold capitals, no matter where you are. The downside is that also conflicts with every mod that tweaks the carriage system, causing CTDs as soon as you walk into a cell with a carriage (this burned me, and had me stumped for days trying to figure out what was causing it).
Honestly though, IMHO most of the changes are good ones. The vampires you fight are much tougher now. Not for the low level character at all. It really feels like a challenge facing them. So now they feel like Big Bads. While I mourn the loss of the Scenic Carriages mod, I do appreciate what they did to improve the carriage system overall. Plus the face-changer that DG adds was long overdue. That should have been in the vanilla game. I personally think the good things outweigh the bad ones.
Edited to Add: Oh, yeah, and as DE notes, no one hostile to vamps at stage 4 anymore with DG. People only become hostile if you turn into a vampire lord.
This post has been edited by SubRosa: Feb 7 2013, 01:40 AM