I say that because it is pretty lame but was terribly ambitious at the time it was released. This movie came out in 1963 and had what was considered at the time to be a ludicrously high budget of $3 million. Unfortunately, despite their intentions of pushing the limits of special effects that existed at the time the movie managed to not make back its budget until years later.

I was not alive for a long time after this movie was created but did end up seeing it as a kid in the 80's. Certain scenes from the film still (kinda) held up in this time such as when they were fighting skletons or giant something or others.

i'm guessing that is Poseidon
Now before anyone gets too judgy-pants let us keep in mind that it was 1963 and there wasn't a whole lot in the way of CGI at the time. I don't think there were any computers outside of the ones they were using at NASA and those would all fit inside your micro SD card slot in your smartphone by today's standards. Therefore, when you consider that they had almost no technology to use, this film is pretty epic. They had to be extremely creative in order to pull these sequences off. The actors who were dealing with any of the mythical creatures had to be filmed fighting nothing and just guess where the claymation people would end up overlapping the second set of film that would later be put int.
That's pretty remarkable when you think about it and I would imagine it was unbelievable frustrating to deal with in the early 60's. Hell, it would drive us all crazy now even though we could probably snapchat a better film than this in an afternoon.

Basically, you should see this if you want a piece of history. The movie was largely well-received and it has become a cult classic that continues to pack late-night showings at theaters around the world for what can (and should) be considered truly revolutionary film techniques of the early 60's.
The film is based on Greek mythology and although it breaks from being exactly accurate on many occasions, it is widely regarded as being as accurate as can be expected given the film techniques that existed at the time.
If you go to watch this movie expecting it to be comparable to any sort of special effects that we have these days you will be disappointed. Go into the movie understanding that it was made OVER 50 YEARS ago, and you will be pleased and delighted at the film these guys were able to accomplish given the fact that they had almost no technology available to them at all.