Darius: there are NO new textures for the old client. None of the visual "pretty" that you'll get in AC:ToD. Also the HUGE lack of content. There is quite a lot of COOL content in AC:ToD which you will completely miss out on if you don't purchase it. Just like you'd miss out on the Queens quest, or the Pincer quests if you didn't purchase AC

M. Also all of the items that come from the Expansion are marked "Expansion Only" which means that you cannot have/use those items unless you purchase the Expansion.
I personally think of the expansion more in terms of what AC was to AC

M. AC

M was a large content patch basically, which is the same for AC:ToD.. the difference between what happened with AC

M, and what is happening with AC:ToD however is that they have gone BEYOND just the large content update, and have actually upgraded the client, and textures. Sure everyone gets the new client, but there is a lot you'll miss out on visually and content-wise if you don't purchase the expansion.