Voyage Into Space is very entertaining, despite the fact that it (a) was cobbled together from episodes of a series, (b) has some of the most mediocre special effects that you've EVER seen, and (c) has a highly repetitive story arc. What it lacks in quality it makes up with in imagination, and in the friendship between "Giant Robot" and the young boy, Johnny Sokko. It's a classic good (Giant Robot, Unicorn) versus bad (Guillotine, Gargoyle Gang) plot. But there are twists and turns, and you're never quite sure who will come out on top.
I'm not a rabid Japanese movie fan, and I wasn't really big on the monster genre. But this one captured my attention so much that I saw it (literally) 20 times as a kid. I mean, what kid wouldn't want a practically indestructible giant robotic friend that followed your commands? It was fun.
A side note...Months after meeting my (now) wife, we discovered that we'd BOTH seen this movie a jillion times as kids. We also argued for years over the Unicorn salute. Finally, we managed to buy a copy of the movie. Darn it, she was right on the salute. But I'll tell you, it was really fun to see that movie again. This thing was not high budget, but it accomplished something that many sci-fi blockbusters can't do today - it was memorable.
The many websites for Giant Robot and Johnny Sokko let me know that there are others who, after all these years, still remember that crazy movie like I do.
If you can, see it.