The is the benchmark for any MMO expansion
The 2 new races have interesting stories that make playing as the Blood elves or the Draenei much more interesting. You won't be feeling playing as them boring and the classes they allow you to choose are no where near the same as the other races in your faction.
Outland has many new interesting features, the surroundings feel like their of a different dimension from Azeroth and it is. Then something that is unique: the ability to use a flying mount to fly. And your not flying across a short area of land too. Flying from above and looking down you'll see some lovely grpahics from above. There are new quests a new city that's neutral and much more.
Also there's the new battlefield: Eye of the Storm and this offers a different way of battling, however it is not the best battlefield as it lacks in features but still the graphics again are amazing and a flag based battlefield hasen't been created yet and is still good.
Overall Outland does lack in a bit of features but still it's a must have expansion to any of those who have the original WoW. You will not be dissappointed.