Used to be a great company to work for 6-7 years ago, but no longer. Once you are beyond the initial excitement of flying a 747 (which can happen quickly), you will find quickly that being away that much is destructive to your family live.
Having that said, it entirely depends on your circumstances. If you don't mind being away a lot and want to live in or around rainy LUX, then it might be OK.
If you have -or plan to have- a family and commute, then the chances are, that you will not be happy there.
On the positive side, the training and atmosphere is good and the job is relatively secure.
You may however want to get very familiar with what I would call the "Luxembourg Factor" which is very unique, but that has nothing to do with Cargolux itself.
other than that corporal klinger's statements all all correct (first hand this time)