Shift work, different situations, challenges, colleagues and passengers every day....no day is the same.
Being in contact with people from different countries/different cultures. Interest in taking care of these people. Feeling that anywhere in the world isn't that distant after all and that you're a world's citizen (if you know what I mean).
Flying itself-absolutely love it! Also I love aeroplanes and their typical smell....though the stink of some 737/757 can be revolting first thing in the morning, but it's part of the deal
Human relations are the most important part of this job. I believe any airline wants to see that you naturally take a genuine interest in the passengers' needs.
Good luck!
FBW