Star Wars
A very well known series but one that I have always loved. That is not to say I love every part of it though. See My Star Wars Watch Order for the films and TV shows I think are worth watching in the order I think you should watch them.
I think the best parts of Star Wars present a unique setting in a way that makes it feel believable even though it is fantastical. I would describe it as Science Fantasy rather than Sci-Fi because of various elements such as the force and the lack of any real hard physics based stuff.