If you read your dream symbolically - the mountains can represent struggles, and the giants could be men who are capable of handling the problems. Some could read the dream with erotic undertones, massive giants tilling mother earth, doing with her what they please, which would reflect back on how you feel about yourself as a male (since you don't see yourself as a giant in the dream). Fascinating dream in either case.
One theory is that your brain is trying to make sense of a bunch of random stimuli. Another is that during dreams your brain is trying to process experiences you've collected during your waking hours. Try to figure out for yourself if you've been busy with a lot of fantasy stuff or something. I don't believe dreams have some magical, future-predicting, divine power or something like that, so in that sense I think it means nothing at all.
Then it is probably just a note about how everything around you is changing with the times and your subconcious is not bothered by it. As for the giants, going off of one of your previous posts, it is probably just something that Shadow of the Colossus slipped in to take place of something. I honestly wouldn't worry too much about this dream unless there is some kind of emotional impact it had.
Damn that sure is a trippy dream. I would interpret it as... there's things in this world that is bigger and more important that us, that keeps life to change? Giants once were gods that shaped the earth? Change is inevitable and controlled by something bigger than us?