Congratulations in English is a simple, easy way to do convey all the possible emotions.
Out of the 200+ congratulations I've received in person and online, almost all people said "mazal tov!" to me, and I think that's appropriate. However, a surprising number of people followed that with, "Is that what I'm supposed to say?" Do people say it because it's the default thing to say about something joyous?
Two very smart friends suggested that mazal tov is not the appropriate phrase. They argued, and I think rightfully so, that the "more correct" phrase would be "yasher koach."
What say you?