To contrast with the giant monster genre, look at The H-Man, a slower-paced and almost subtle (in this genre) take on a strange series of disappearances. The people that go missing leave only their clothes behind, and it all is tied in some way to research on radioactive explosions. The inevitable scientist makes his appearance, and things start to heat up with the emergence (finally) of the monsterous threat. The H-Man showcases the extent to which Toho really did a great job of building tension, without relying on special effects or men in rubber suits. Sure it's vintage, but that doesn't make it any less creepy all these years later. The opposite side of the spectrum is Battle in Outer Space, with lots of superlative special effects that are really the only thing going for the film. The story of alien invasion was much more novel when Battle in Outer Space was made, and what's really wild is how naturally we are presented with the picture of Japan fielding an expedition to outer space. Waging war on aliens is always a dangerous proposition, and Battle in Outer Space does a nice job of depicting some fairly epic battles.
The key to enjoying these films is to recognize that they were incredibly exciting at the time, new visions that were defining a unique style from Japan. The copy-cat films that would follow, made in Japan and in the US, were sometimes good and sometimes bad. These three are a nice sampler, something for anyone that considers himself a sci-fi fan. The H-Man resists the sci-fi label but may be the best of the bunch, in terms of raw quality and punch for the viewer. The Toho Collection would be better with more special features and historical reference points, more detail on how the studio came to be in the right place at the right time, with the right talent. Commentary included is good for atmosphere, but light on the distinctive manner in which these movies were made. Including both English and Japanese versions of the films seems largely a waste for fans that will favor the original issue and subtitles. The experience back then for Japanese audiences would make for an especially nice historical study, but watching these old films through modern eyes is still highly entertaining.