If you've read my review of Dark Souls, you'll know I absolutely love the base game, and the amazing gameplay hasn't changed for this expansion, so that's still great. With all the rich history of the world presented in the base game, this DLC had a lot of choice for which part it could focus on, and Artorias and how he became known as "The Abysswalker" was certainly not a bad choice, as there are a few new interesting NPC's around that add even more to the lore.
There's cool new weapons and items, and every new boss is surprisingly great. With the base game's hit-or-miss bosses, I was expecting there to be at least one stinker among them, but no. They're all amazing.
HOWEVER...adding a PVP arena as part of a optional DLC was dumb. Really, really dumb. It means only a small percentage of people who own the game (those who bought the expansion) can use it, and therefore the player base was pretty small to begin with, and it died off quickly.
As well as that, unfortunately, I didn't like the design of the new areas all that much. While there were a few stand-out bad ones in the base game, in this DLC, there's only three substantial ones, the Royal Wood, which is literally just the Darkroot Garden with a few tweaks, the Chasm of the Abyss which is just a series of dark plains, and the Oolacile Township, which is actually good.
It's a shame considering the amazing design of nearly all the areas in the main game, but it doesn't ruin the amazing new bosses and interesting characters, or the brilliant gameplay of the game as a whole, so it's a pretty standard expansion recommendation: if you like Dark Souls, you'll like this.