They made a real effort
Given the technology available to the team making this, for the budget they had, they tried. Some of the effects, with the giant, as not great, not even by the 50's standards. Certainly it looks hokey to us.
As they were using a man for the colossus, they could not use a stop-motion miniature as King Kong, and I think the movie suffered for it. They didn't even make a hand to interact with things on the ground, and it was a bad choice.
It isn't a bad movie, but it certainly could not live up to Kong, doing the same giant-things.