"Is it worth ..." questions need a predicate. What do you value as worthy?
In this case, does it mean, I want to sell more books, so if I spend time on Goodreads will I get more sales?
Or it could mean, will I learn more about the craft of writing here?
Or it could mean, will I find a community of fellow writers (or readers) with whom I can talk shop?
and so on.
Obviously there's worth at Goodreads. Folks have mentioned a few points. If it were worthless, no one wouild go there, right?