i can still feel the bumpy box from this image
they expanded upon previous ideas, added a bunch of stuff, added a whole new area, flying mounts and multi-person mounts, etc.
best of all, they added glyphs, socketing, and a better enchantment system. really allowed for some amazing customizations
fantastic expansion, probably the peak of WoW for me
One of the best games I've ever played, if not the best. Irrational Games knows how to create a great immersive experience by taking the immersive sim concept Looking Glass was demonstrating with their games, and merging it with a complex FPS-RPG system where you can almost create a completely unique character everytime you play. Also, the storytelling is superb, with some thoughtful commentary from people in the game (with the help of audiologs you find while exploring the spaceship where you're trapped), and SHODAN. The opressive atmosphere is amazing too, the soundtrack fits very well with the places you visit in the game.
Nothing more to say, this game is a must.