I think what I find challenging is just trying to bring a truthfulness and a realism to a character.
The most important thing, when playing characters with chemistry, is being able to work off the other actor and be supported.
As an actor, if I just did sci-fi, I think it would get limiting, like if you just play lawyers or doctors, over and over. It's a lot more fun, if you get to play lots of different types of characters.