Was so happy on the AddOn and was not disappointed. The new classes, etc. increase the replayability simply immense. The new opponents complement beautiful and extend the whole main game again. Finally a AddOn bring the one to again play the main game really long and motivated.
All that should strike with Enemy Within played no XCOM my opinion now. The only thing that bothered me a bit was that I had to download for some reason 6GB again, but you could easily do so overnight. ;)