If you like metal gear online get this expansion.
You get 3 new maps (OO, RR and HH) and the ability to play as Vamp or Raiden (you also get the option to purchase SCENE only gear.......but who cares about that ¬__¬).
The 3 new maps are very nice and probably the best ones I have played. They are highly detailed and allow for some excellent flanking/manoeuvring.
The new characters are also easily the most fun special characters available. Raiden can deflect bullets and Vamp can resurrect wherever he was killed. Vamp must be played more stealthily whereas Raiden is more head on.
Again, all I can say is that buying the expansion adds a lot of value to MGO and will make it much more fun. If you have spent over 100 or so hours on it then I recommend you buy this expansion.